The LP is important for implantation. Given you're also losing weight as well as having a shorter follicular stage, I'd go get tested. I have no idea if the thyroid is involved in weight loss, but it can affect fertility. Unexplained weight loss should be investigated.

I'd ask for a CD3 test for estrogen levels as well as a 7DPO test for progesterone. The should also include FSH levels. My understanding is if your estrogen levels aren't high enough to ovulate, then this will affect the corpus luteum/progesterone levels.