Not sure if it is implantation bleeding.

Hi there. Im really confused and i need some advice.. just going to apologise in advance for any graphic info :) but i have irregular periods. I have suffered two miscarriages in the past 2 years. First baby was at 13 weeks. (Found out at dating scan there was no heartbeat) and i had to have a pecissary to induce contractions to miscarry. As heartbeat had stopped at 8 weeks. Second baby i naturally miscarried at 7 weeks. And now according to ovulation calculator online i ovulated on 12th may. Me and my partner had unprotected sex on that day and also every other day around that time. I was due to Implant on the 20th may. I started getting mild cramps and headaches on the 19th may and also i have really sensitive breasts. I had really light brownish discharge for one day and then moderate heavyness with red blood for 2 days then it was light brown again on the last day so in total 4 days. Usually i have a really heavy period for 5-6 days of unbearable cramps. Could i be pregnant?