bleeding after period

So I've had this a couple times since having sex in September. I'll have my period (late thoguh) and then I'll bleed randomly throughout my entire cycle. Like my AF ended over a week ago and suddenly I have these cramps in my uterus area resembling period cramps and I'm lightly bleeding, is this weird? No I'm also not pregnant! Been having fluttering in my heart for a few days now and lightheadedness which I've had since October