Invalid bfp, then bfn, then pregnant?

I tested with a first response yesterday (think at 9 dpo - I don't know exactly the number). After the 3 minutes i didn't see any line. Went back to bed and after I got up I went to check the test again and there was the second line. Of course that's usually an invalid test. Got a cheap test from Walmart and tested today bfn. If my math is right today is 10pdo and I know too early. Bad has anyone had a similar experience and ended up being pregnant? I'm just trying to hold to any bit of hope. I want this baby sooo much!!! Thanks ladies for taking the time to read and respond. I started feeling a very light cramps last night and have it this morning. I'm super emotional... ❤