Thoughts needed! Tests dried positive?

I just had my son 7 months ago. Since I stopped breastfeeding at 4 months I've only had one cycle in June. It was heavy and lasted my normal 5-6 days. When July came around I had spotting. Started off light and brown, than some pink/red, than back to brown. It never got heavy. This only lasted 4 days. At first I thought it was just my second period, but than a few days later I woke up very nauseous so I thought implantantion bleeding??. (I had terrible morning sickness with my son) so I decided to take a test. It was SUPER faint that I thought I just had line eyes. The next day I was nauseous again, took another test...same thing just thought I had line eyes. I had kept both the tests and out of curiosity I pulled them back out. Sure enough I saw two lines now that the tests were dry. I know they are invalid after the timeframe but any other time in be past I took a first response test they never dried with a line. So I thought id take another test yesterday morning, and within the 3 min I saw the very faint line but this time I knew it was there. So, today I took another test but I was out of my first response so it was a cheap hcg strip test and saw nothing??? Can it be normal to get a faint line on one brand, and nothing on another? I primed more first response tests and they should be here in time for me to retest Thursday morning. I'm just not sure what to think right now?

To add, it's been a weeks since that spotting episode has stopped.

Top test is the very first one I took, bottom is most recent

Tests that dried "positive"

This picture was taken within the 3 min on my latest test

2 days later with afternoon pee taken within 3 min???...