confused

So I went off BC in December of last year. I was having pretty regular periods but then April I had a period that was about 3 weeks long on and off. Then May a regular period again. But since May I've had no period. A little spotting here and there but only when I wipe not enough to wear a pad or tampon. I've taken 4 or 5 pregnancy tests that were all negative. I've read online of women not showing on a home pregnancy test but only on a blood test. Has this ever happened to someone where only the blood test showed positive? I'd like to think this is what's going on but my appointment isn't until the 22nd and I doubt I'm pregnant. just wondering if anyone's experienced this?