Short luteal phase - help

[firsttimemummy321]

I've been referred for recurrent miscarriages (early losses) because for the last few months I've had positives tests but bled before/after and they've not stuck.

Some bleeds have been with no positive at 7dpo others with a positive around 10/11dpo.

This morning I got a faint positive on a cb early at 8dpo (no other brand as didn't have chance so not 100% I trust it as a positive as was a shadow the after the time limit was clearly blue)
And now I've just started bleeding.

What could be causing this? Are the pregnancies self aborting super early and that's causing it or is it more likely the short luteal phases causing the losses? 😩

Note to add trying for our second of that makes a difference

Oh also still breastfeeding my first but only for comfort and nap (14 months old so mostly on solids now) dr said this should affect it when I asked about it a few months ago due to baby's age and how often baby is feeding

Anyone? 🙈