Confused about my cycle

I had always regular cycles so no issues with PCOS but i am confused with my LH surge going up and down and when to time BD! it is our 5th months TTC and I have already done ultrasound and Hormonal tests except Progesterone ( waiting to do on CD 21 and those tests came good). Not sure what’s going on.

In my Feb cycle, I had LH surge on CD 16 cycle length was 27 days) and in March, on CD 16 i had not still got my LH surge ( cycle length was 30 days)...

Any body had the same issue here?