Why do I feel cramps in my uterus days after my period?

[mcatb]

I've been on birth control for about 10 months and the last time i had sex was two weeks ago. I had my period last week and ended on sunday and started back on my pills on monday, but a couple days after i've been feeling cramps in my uterus. It also feels very full. I have read somewhere that these are symptoms to implantation but that doesn't happen until 14 days after the period (during ovulation), which is why i don't think it's pregnancy, but if it's possible let me know or if there's another logical reason on why i am feeling this please reply!