am I pregnant ???

So I am 14 weeks postpartum and I got my period in may. This month I started feeling that groggy and crampy feeling .. thought it was my period, but thought I would test just in case (I drink a few beers here and there) well, took one last night and it came up a vf positive and this morning I took another and it was negative. Anyone had this happen ? I'm going to retest tomorrow morning .. but I thought it was strange one was positive and the next was negative. Last pregnancy I was already almost 12 weeks so the positives just kept coming lol. Thanks in advance for any help/advice !