Positive pregnancy test during period

I felt pregnant all month. My period occured on the fifth of january and I had unprotected sex on the 19th or 20th which I believe is around the time of my ovulation. I was sooo sure. I bought a home pregnancy test that had an extra strip. I tested first on the 31 and it came up negative. I was getting ready to take the final test to be sure right after I missed my period. The thing is - I got my period. Right on the fifth, like normal. Today, just for the heck of it (and also to get rid of the test - I mean I paid for it, might as well get my money's worth) I took the second test. It came up positive. Now I'm confused. I looked it up on the internet and there were two possiiblites a. miscarriage or b. ectopic.. Neither sound very promising. I'm so disturbed - I really wanted this baby. If it's a miscarriage will I be able to get pregnant again? The same with an ectopic? Is there a chance that I might have gotten pregnant right before my period and not realized it? (note: I have highly irregular periods because of my thyroid condition)