Me And My Boyfriend Been Trying To Conceive, And We've

Me and my boyfriend been trying to conceive, and we've been having unprotected sex. Recently, I've been feeling tired a lot, feeling nauseous in the mornings but never throw up and been having cramps. My ovulation period was from the 7th up until the 13th and between that time i believe he ejaculated in me. But, then on the 18th he ejaculate in me as a planned experience. Then, on the 21 of this month, I experienced a brownish greenish discharge, then the next day I started to bleed lightly; then heavy as the days went on. But I was stunned because I wasn't scheduled to get my period until the 26. So I want to know could I be pregnant and suffering from having a heavy implantation bleeding?