If conception date was 2/28/2015 how far along would I be now? I didn't miss my period on 3/12/2015, but took a positive pregnancy test this morning

Last period? Pregnancies are not dated from when you think you conceived but from the day the last normal menstrual period started. Assuming you did conceive on Feb. 28th you'd be close to 4 weeks 5 days today (3/19/15.) Good wishes.