Late ovulation and levo?

Werdah

Hey ladies. Ive been diagnosed with hypothyroidism and was previously diagnosed with Graves disease last year. this is the first month I'm taking Levothyroxine as per my fertility specialist recommendation. I started taking my meds on CD 13 as that's when I was diagnosed. I have always ovulated on CD 17 (opk and temps confirm) but this cycle I had a positive opk at CD 15-16 with Ewcm but when I had an ultrasound at CD 20 it's showing I haven't ovulated and still have a follicle at 28 mm. I'm worried. Are the thyroids med causing this? Am I not going to ovulate? Did any of you ladies have this problem? What was the outcome?