Help???😳

OK ladies! I found out I was pregnant early at 2 1/2 weeks. I got all the way to four weeks and started to miscarry. Two weeks went by and I had no blood. My cycle is not due to start until 5th of February. yes, I had sex right after the miscarriage. I’m not sure what’s going on, due to me last night starting to bleed. I took a first response test (before the bleeding wart in the day and it showed up positive with two bright lines. I didn’t think much of it because I know sometimes, the hormone level will still read pregnant being that I just was pregnant four weeks ago. I tested again this morning and the HCG test was very very faint. Can somebody explain how the test went from dark on a first response test, then light on an hCG test within 24 hours😳 I was told that I could have gotten myself pregnant right after the miscarriage. Is that possible???