Pregnant test question please help!!

Mayra • 30 pregnant with rainbow baby
I've never had this happen. Since last week I have taken 6 pregnancy test.. Last one today. The test read a positive result and withing a min it disappears and reads negative. All 6 pregnancy test have been the samw. Ive done some reading on the web and similar stories and most of them end up being pregnant. I dont want to get my hopes up but its hard not to 😓. Has this happened to any of you? I'm making an appointment tomorrow with my Dr. Just a bit of info about myself. Periods are always irregular so I really don't know when I'm ovulating or not. Last month AF came from 7-8-15 to 7-11-15 had intercourse on the 18th and 23rd. Of I were NORMAL I would be ovulating on the 23rd right? There is a chance right? 😓