Yet another miscarriage

I got my first BFP on 5dp5dt and I was feeling so hopeful. Lines were slowly getting darker and I was praying for a high beta today 13dp5dt. My line wasn’t very dark on 10dp5dt but so many reassured me it was good, I held onto that.

Today driving to my beta I felt in my gut it was going to be bad news and it was..13dp5dat and my beta was 18.5.

Yet another chemical, 3 in a row now and I have no idea where to go from here.

Hubby and I are 26, healthy and diagnosed with unexplained secondary infertility..just doesn’t make sense.

Any suggestions on next steps? What tests I should request? What could be the issue? I’m absolutely devastated :(