Hi Babyluv,
You have a really short luteal phase just like me (I'm between 4 and 8 days)! My first bit of advice is if you've been charting your cycles take all evidence possible to your FS appointment. I've had trouble getting 2 different specialists to believe that my short LP is true!

I now use progesterone pessaries twice a day from ovulation and consistently have a 13 day LP when using them. Also, I had a lot of spotting during my luteal phase so had a laparoscopy and d&c to check it out. The d&c stopped the spotting and the progesterone lengthens the luteal phase

Hopefully I haven't scared you - you probably won't need any surgery but maybe just progesterone supplementation. Oh - and I tried vitamin B and vitex but unfortunately it made no difference for me.

PS - I'm really encouraged hearing that you've had a healthy baby. Thank you! Sorry for your losses