Dominant follicle, delayed period.

I'm 33 yrs old, married & trying to conceive.My last period was on 29th October and I have irregular menstrual cycle (30-40 days). last menstrual cycle was of 30 days.I have hypothyroidism and I'm on medication.I don't have PCOD. Yesterday on 28th October I have done USG.A dominant follicle (18 mm) is found in my right ovary. I'm so much surprised because I thought my ovulation is over as I had been tracking Cervical mucus & observed fertile egg white mucus on 14-16 days on my cycle and had sex .Now I am experiencing PMS...how can I experience Pre menstrual syndrome when ovulation is not over?or is there any possibility to have dominant follicle after ovulation? I'm so much worried and anxious because both my husband and I reside in different cities.we meet very rarely. it's very important to track the ovulation time but it's not happening.. Please help!!