Mirena crash? (breakthrough bleeding)

Hi,

I'm really going crazy and feeling so insecure about my body! I'm looking for answers, but I can't understand why I suddenly have breakthrough bleeding.

I stopped using the IUD two and a half months ago to try for a second baby. While I had the IUD, I bled every 30 days, so I know how my cycle works.
With my first baby, I got pregnant immediately after the IUD was removed.

In the first round, we used full protection. If I had gotten pregnant, the due date would have been too close to my daughter's birthday, we thought. Didn't think it through well enough Very short period, but bleeding on the expected date. By the way, I got my second Corona vaccine on my period day. So maybe that also affected the duration.

Second round: ovulation on day 14, but period started one day early and was heavier than usual (although still just 4 days).

Now in the third round, I haven't ovulated yet on day 15, but what's making me insecure is that I've had breakthrough bleeding for two weeks!

The first bleeding started 8 days after the first day of my period and lasted three days (two days with half a tampon, third day very light flow).
The second bleeding started 13 days after the first day of my period and has now also lasted three days (light flow all three days).

Now I read somewhere about a Mirena crash, but it doesn't seem like I'd suddenly still be suffering from that now.
But what are these breakthrough bleeds then? And does it affect my chances of getting pregnant this month?
Does anyone have experience with this?

These bleeds are making me so insecure!