Bleeding help please

I bleed while on the bc shot. once i get it im fine for about 2-3 weeks but after a little i get terrible cramps and my period wont stop till i get my next shot. sometimes i have to take the birth control pills at the same time just to stop the bleeding. what should i do? the cramps are unbearable and whats the point of being on bc if im always bleeding. should i stop or switch? what should i switch to? pills are not an a great option i will forget to take them. comment please