Waiting for my Doctors Appt next Wednesday but I'm not even sure what's going on.

So my June period was normal started the 5th. Ovulated around the 22nd. Negative hpt all the way to July 6th. Started bleeding July 7 through 11 lighter than my normal period but heavier than spotting. Took it as my period. Went on Vaca didnt test ovulation and hpt till July 17 had a faint positive on my hpt and positive ovulation. I've continued to test and they seemed to get darker but then go back to faint.

HCG level on Monday (July 22) was 42

HCG level on Wednesday (yesterday) 39

Has this happened to anyone? Not sure what to expect? Was it a chemical? I dont understand how the pregnancy tests before my vaca didnt pick it up.