Period? and still preg

So on Saturday I thought I got my period, Sunday had it...now today it's like nothing. Maybe a super tampon full.I'm on letrozole every day, 2.5 mg, trying to get preg for about a year now ..my doctor has me going every 21 days to check my levels...now before I got my period Saturday my boobs were sore, had side pains ..I thought early preg symptoms..?.I'm on my 3rd cd and it's like nothing. Usually last 5-6 days. ..could I still be preg? Does that pill make me have negative pregnancy test?! So many questions ...help.please.