Been Ttc for 8 months

Kami

Okay ladies I had my mirena iud our in December and have been ttc ever since. I had 2 regular periods after and then missed 2. I was supposed to start my period on August 4th and haven’t yet. According to this app I’m 17 dpo and supposedly ovulated on the 20th. I had intercourse that day and on the 18th. I also had intercourse on the 25th. I didn’t get my period but on the 5th and 6th had light pink spotting when I wiped. And mild cramping for a brief amount of time on both days. So my question is could I have been ovulating closer to the 25th instead of the 20th and could the light pink spotting be implantation bleeding? I have taken a pregnancy test on the 5th and this morning with a bfn. So I’m wondering if I ovulated later than the app says and that’s why I’m getting a negative result. Online I read you should wait 2-3 days after implantation bleeding happens at the earliest to test. Does anyone have a similar experience and end up being pregnant?