Could I be pregnant or is it just my period trying to come

Britney

I’ve had an headache for a week now, I also had unprotected sex from the 31st of last month to the 11th of this month. I’ve been experiencing cramps just on one side, then it will go to my back. Well I thought my period was on because I bled on Monday of this week... which was only one time. Since then I haven’t seen nothing else. My cycle is irregular so could it be my period trying to come or could it be implantation bleeding???