Do Light Periods = Infertility/ Implatation issues ?

Ladies, I need help? Please. My husband and I Haven been trying for three years now to conceive. Naturally and with IVF. Three embryo transfer fails now.

I have super light periods like 3 days max and I only usually need one light tampon a day. I feel like this isn’t normal. And could mean I don’t have a thick lining. Which could be the cause of the implantation failure. However the endocrinologist always said it looked thick enough for the transfer.

I’m afraid to do another one without getting to the root cause of my light periods. (Also, I had the IUD for 5 years but it’s been out since 2019).

Any help? Advice? Insight?