A lot of things can cause hair to weaken. It could be a lack of iron, do you take vitamins daily? However, what a lot of women don't realize is that it can be their shampoo that is damaging their hair. May I ask what shampoo you're using?
Also, perming hair is extreme, that's why they won't dye/perm your hair at the same time at the risk of intense damage. It could also be so many other things, straightner, hair dryer, if you live in really hot weather, sun damage. I would start eliminating other factors before blaming the pill.