I just finished a cup of green tea with some matcha after lunch and almost dozed offfelt sleepy for a while, as usual.

Your Japanese text says "I felt sleepy for a while"

I started using the matcha yesterday because I heard theabout its health benefits of it, but apparently I didn't use enough of it for a caffeine intakeboost.

I have to be careful about caffeine, though, since I have difficultiestrouble falling asleep every night.

It is also torturous when gettingvery inconvenient to be sleepy at the wrong time, isn't it?

(Intended to be casual writing) ¶
I hear it's natural to get sleepy after eating.

English actually has a colloquial term for severe cases of this: "food coma." For example: "Man I had such a bad food coma after lunch, I think I ate too much."

I just finished a cup of green tea with some matcha after lunch and almost dozed off for a while, as usual.

I started using thedrinking matcha yesterday because I heard theit had health benefits of it, but apparently I didn't usedrink enough of it forfor the caffeine intto keep me awake.

It is also torturous when getting sleepy at the wrong time, isn't it?

I never hear "torturous" in casual speech. I might express this informally like this:

"It's such a pain to get sleepy at a bad time, isn't it?"

The key to making this sound casual is in how you express "bad". Here are other ways:

"Such a drag when..."
"So annoying when..."
You could also use swear words when in very familiar company, though be careful.

I just finished a cup of green tea with some matcha after lunch and almost dozed off for a while, as usual.

The sentence is good! However, when you say 'almost dozed off', it sounds like you mean 'almost fell asleep, but didn't'. If you did sleep, it might be more natural to say 'dozed off for a while'. If you didn't sleep, then it makes more sense to say 'almost dozed off'.

I started using the matcha yesterday because I heard theabout its health benefits of it, but apparently, I didn't use enough of it for adequate caffeine intake.

'Caffeine intake' or 'adequate caffeine intake' sounds a little too formal for casual writing. Sometimes people say 'a boost of energy'. So, I might say 'I didn't have enough of it to get a caffeine boost', but your sentence is good!

It is also torturous when getting sleepy at the wrong time, isn't it?

It is also tortuous to get sleepy at the wrong time, isn't it?

I just finished my lunch with a cup of green tea with some match after lunch and almost dozed off for a while, as usual.

I am not sure what you meant by “with some match”. Did you mean matcha?

I started using thedrinking matcha yesterday because I heard theof its health benefits of it, but apparently I didn't use enough of it for the caffeine intake to take effect.

I assume you mean matcha?

It is also torturous when gettingyou get sleepy at the wrong time, isn't it?