BBT chart confusing and temps look too low?

If anyone could help interpret my chart, that would be much appreciated. I haven’t consistently recorded each day but, having read about average bbt, my temps are lower than average. From CD 14-28, my temps seem to be lower than what the average bbt should be pre-ovulation. Also I’ve had a lot of fluctuation post ovulation. AF due tomorrow. Not sure whether to go to GP to get tests for thyroid/low progesterone. Any advice would be great. 4 months TTC and no luck! Thanks!