Ihave the swimming unit in school in around like 3weeks. if i do 100 squats a night and 50 sit ups would it make that much difference after 3 weeks? like would it be noticeable?

maybe If you work super hard

Explanation:

I guess

I would suggest you go for about 10 sit ups and 5 push ups in the first few days, to get adjusted to the routine. it's not healthy to jump into a hard work out at once. after a couple of days, you could keep on increasing the number of exercises.

I would also suggest you to try wall sits and jogging. skipping is a good way to regain your stamina. I would also like to say that planks are a good alternative for push ups. start with 30 seconds, and keep on increasing.

These exercises would help in losing wait, so it is necessary that you have your diet planned. make sure you take proper warm ups before you start your training everyday. water is essential for the work outs.

hope this helps your training. don't worry about the consequences. I'm a professional athlete and I've been trained hard. this is a start. don't worry about the muscle cramps. just try to breathe freely while working.