Trying to figurenit out

So my son was born four months ago and I bleed the whole damn time I just stopped bleeding 3 weeks ago and when that happened me and the hubby did the deed lol but before I left the hospital I had gotten on the deposit shot but I was do for it in September and never went back to get it now I'm wondering if I could be preggo it's been 3 weeks since we had sex and not sure if it's my period coming or implantation due to the fact it's very light only when I wipe I feel alittle off like mikd headache and very small cramping if it's not my period I'll be alittle worried