Period cramps!

So I'm 14 and today I got my period as usual (it comes same time every month) it used to be very heavy when I first had it, and now it's very light but really long! It lasts 8 days. But when it used to be heavy I never used to get cramps, but now it's light I get cramps, back ache etc! Why could this be? Also what could help with the cramps apart from a heat pad (it's 20°c rn and if I get any hotter I'll be ill!) thank you for reading this xx