I have been using multifilament strings for a long time but i have noticed lately that my shots get outside the court a lot when i hit harder so would it be better for my case to switch to poly string? I am 17 years old.
I'm not wild about multifiber in general because is seems to steadily degrade as it's played - it seems to progressively loosen up. If I want to have some firmness and control with it after a few hours, that means that I need to install it at a higher initial tension, but that defeats its softness and it can also fray more quickly at higher tension. It's a good option when string bed softness is a high priority, but the premium multis are rather expensive.
Synthetic gut is a good bridge between softer multis and stiffer polys. While it's not terribly exotic stuff, it offers moderate softness, but doesn't turn to mush like multi can after some use. It's tension maintenance over its service life is usually pretty decent. At least for me, that means that it will give me better feel and control through several outings. If you want a bump in control, this could be an easy option to live with and it should cost you less, even if you keep restringing every 15 hours.
You'd probably be fine using a syn. gut at the same gauge and tension as the multi you're using now. It will likely feel a little more firm and "crisp" compared with your multi, but not harsh as long as you don't increase tension by more than a couple pounds.
Jumping from multi into poly is a substantial move. I don't recommend it without trying syn. gut first. But if you do dive into the poly options, I'd say try a hybrid that includes a relatively light gauge poly main (maybe 1.20mm) and a 16 ga. syn. gut cross. This setup has been very well received among the local sluggers like yourself who have me string their gear. I've been coaching a local high school team for several years, so I eventually took up with stringing, too.