Can Follicle Rupture After Day 20 Of Taking Clomid?

Hi, I am on day 19 of my cycle, first time using 50mg of clomifene. I have been going for vaginal ultrasounds every couple of days and I had 1 follicle started on day 9 at 13mm, then 2 days later went to 17mm then 19mm and has stayed at 19 for 5 days now. My lining has increased to 8.5 from 8 a couple of days ago. The follicle has still not ruptured yet. I have been told to ring the clinic on day 40 if I have not had a bleed. My bmi is normal, I am healthy, my natural periods were every 5 weeks approx, I came off yasmin contraceptive pill 1 year ago after being on for 9 years and have not had a natural period since. I have had 3 courses of progesterone pills to bring on a period and then I was prescribed clomifene. I do not have anything wrong with my tubes as I had an xray and have had blood tests and all that was found was my estrogen was low.
Please can you tell me if there is a chance the follicle could rupture after day 20 after taking clomid as I was told a lining of 8.5 is good?