Looking at your last cycle, I'd say you had a very short LP. The lining wouldn't have had time to build up.
I suggest getting some basic blood tests. Get one at CD3 to test estrogen and FHS.
If your estrogen levels aren't high enough, the egg usually isn't great, meaning the corpus luteum isn't great, therefore you don't produce enough progesterone, therefore lining isn't great, therefore implantation is difficult....etc.
Also get one at 7DPO or CD21 to test for ovulation.

GL