mMath is hard in high school. :( Math is hard in high school :(

mMath is hard in high school. :( Math is hard in high school. :(

Lately, I have been sturdying math. Lately, I have been studying math.

The perfect progressive verb tense is more suited here as it is an ongoing action. Like 「私は勉強します」VS「私は勉強しています」

Lately, I've been sturdying math. Lately, I've been studying math.

Lately, I've been sturdying math. Lately, I've been studying math.

Lately, I have been sturdying math. Lately, I have been studying math.

It is very hard... It is very hard.

I can't understand it. I can't understand it.

The pronoun “it” (standing for math) is added for clarity as the verb’s direct object.

I can't understand it. I can't understand it.

I can't understand it. I can't understand it.

hHigher order equations are the hardest section in latelmy studyingies lately. Higher order equations are the hardest section in my studies lately.

Formal sentences start with the first word’s letter capitalized.

The section about higher order equations is the hardest section in lately studyingone so far. The section about higher order equations is the hardest one so far.

Rearranged a little to sound more natural

higher order equation the hardest section in lately studyingThe hardest topic lately/recently has been higher order equations. The hardest topic lately/recently has been higher order equations.

hHigher order equations are the hardest section in latelyrecent studying. Higher order equations are the hardest section in recent studying.

"studying" is like a noun (the -ing is like the の in 勉強するの ), so it takes adjectives instead of adverbs.

It makes me (feel) tired. It makes me (feel) tired.

I can't do many questions in my homework. I can't do many questions in my homework.

I can't do many questionsolve a lot of the problems in my homework. I can't solve a lot of the problems in my homework.

"Solve" and "problems" would be the common terminology for math homework

I can't do many of the questions in my homework. I can't do many of the questions in my homework.

I can't do many question ins from my homework. I can't do many questions from my homework.

SThe spring holiday will finish soon. The spring holiday will finish soon.

You can also connect this sentence to the previous one as a conclusion.

SThe spring holidays will finisharrive soon. / The spring holidays will be over soon. The spring holidays will arrive soon. / The spring holidays will be over soon.

Wasn't 100% sure what you were trying to say, so provided two options.