CD 20 - lower tummy aches

I am at day 20 of my current cycle and have been experiencing  lower tummy aches for the last few days. I had a few pains around day 14, although after BBT charting i think i ovulated around day 16/17 (that is when my temp dropped and then rose 0.3 degrees in a day.

I suppose i am expecting an answer of it is the aches experienced before AF. But in previous months, the aches havent been as early in the whole cycle. I would normally have aches initiallly around day 24/25 of cycle.

We have been trying for a baby for 9 months. I have been recording every temp, every CM type, every time we got together, of which has been every other day from CD 5.

Any ideas what it could be.