18 days cycle and Implantation Bleeding

I was wondering if anyone has an 18 days cycle. I’m usually very irregular but since sept my cycle has been every 17-18 days. I was wondering because I knew for sure my period was coming since last 2 nights ago my back was aching so I thought maybe my period will come next day which was mon. I waited and waited and nothing but pink very very small amount when I wipe like almost nothing. And my back was aching so much and that was my indication of period all the time now the pink spotting is gone. But I’m having cramps. I was taking OPKS and never gotten any positive but on CYCLE DAY 12th oct 29th I had an almost positive but it was still lighter than control line so I kept testing but I keep getting negatives so I stopped at Cycle 16. I was wondering if it’s possible that I was having implantation bleeding? And if it’s possible will be able to carry? I’m so scared that if I get a my bfp it will be a bad one again...... I’ve lost 3 angels already been trying for 7yrs