There are lots of mosquitoes during summer in Japan.

Sometimes, I see a mosquito flying in the room, inside my house during the winter.

Maybe,osquitoes can even survive inside of a house if it's warm enough for them to survive even winter.

I rephrased your sentence to use the active voice instead of the passive voice.

I saw a mosquito three days ago, and tried slapping it, but it fluew away.

I've been struggling with itkeeping the mosquitoes away for about three days, but every time I messed up.

Last night, I finally I caught it.

I switched the order of the words "I" and "finally" to make the sentence sound more natural.

I would appreciate it if you could help me sounds more natural, even if you have to fix a full sentence.

Mosquitoes

Both "mosquitoes" and "mosquitos" are correct spellings, but most of the time I see it written as "mosquitos".

Sometimes I see a mosquito flying in the room,around my house during winter.

Maybe, the inside of a house is warm enough for them to survive even in winter.

I saw a mosquito three days ago, and tried slapping it, but it fluegot away.

I've been struggling with it for about three days, but e. Every time I metried to slap it I missed up.

Since this is describing something in the past, "I've been struggling" doesn't fit well since that would indicate that you're still struggling with it.

Last night, I finally I caught it.

I would appreciate it if you could help me sounds more natural, even if you have to fix a full sentence.

There are lots of mosquitoes during the summer in Japan.

Small thing, doesn't really change the sentence but either way works? Id say adding 'the' sounds more natural

Sometimes I would see a mosquito flying in the room, of my house during winter.

Maybe,/ Perhaps inside of a house is warm enough for them to survive even during the winter.

I saw a mosquito three days ago, and tried slapping, it/ but it fluew away/ managed to fly away.

I've been struggling with ithis for about three days, but every time I would messed up.

I would appreciate it if you could help me make my sentences sounds more natural, even if you have to fix a full sentence.

Sometimes I see a mosquitos flying in the room, my house during winter.

I think "mosquitos" sounds better because "a mosquito" sounds to me like you're saying that you only see a single same mosquito flying around.

Maybe, the inside of a house is warm enough for them to survive even during winter.

I saw a mosquito three days ago, and tried slapping it, but it fluew away.

I've had been struggling witying to catch it for about three days, but I missed every time I messed up.

Last night, I finally I caught it.

I would appreciate it if you could help me sounds more natural, even if you have to fix a full sentences.

Mosquitoes

Both "Mosquitoes" and "Mosquitos" are correct.

TDuring the summer, there are lots of mosquitoes during summer in Japan.

Sometimes, I see a mosquito flying in the room, my houseeven see one flying around in my room during the winter.

Maybe, it's because the inside of a house is warm enough for them to survive even wintercold seasons.

I saw a mosquito three days ago, and tried slappingwatting it, but it fluew away.

Usually, you slap people when they're being extremely rude or insulting. The image of you slapping a mosquito is HILARIOUS

I've been struggling with it for about three days, but I missed every time I messed up.!

I would appreciate it if you could help me sounds more natural, even if you have to fix a full sentences.

Sometimes I see a mosquito flying in the room, my house duringin the winter.

Maybe,I guess the inside of a house is warm enough for them to survive even in winter.

"I guess" sounds more natural because the previous sentence has evidence, so you're more confident than "maybe."

I saw a mosquito three days ago, and tried slapping it, but it fluew away.

I've been struggling witying to catch it for about three days, but every time I messed up without success.

Last night, I finally I caught it.

I would appreciate it if you could help me sounds more natural, even if you have to fix a full sentence.

Mosquitoes

There are lots of mosquitoes during the summer in Japan.

Sometimes I see a mosquitos flying in the room, my housearound in my room during the winter.

Maybe, the inside of a house is warm enough for them to survive even (during/in) the winter.

I saw a mosquito three days ago, and tried slappingwatting it, but it fluew away.

I've been struggling with ithis for about three days, but I miss every time I messed up.

Last night, I finally I caught it.

I would appreciate it if you could help me sounds more natural, even if you have to fix a full sentences.