Follicle growth?

Hiya ladies, been TTC for 3.5 years with PCOS and have just started my first medicated cycle. Took Letrozole 2.5mg days 2-6 of my cycle and went for my growth scan yesterday. Was told that it seemed I had only one follicle that had grown but it still wasn’t the size they’d like to see and have advised I come back for another scan in 3 days. My cycle is about 36/37 days so was told this is why I need to come back. Has anyone else had a similar experience, firstly of only getting one viable follicle with PCOS? Secondly, anyone with a longer cycle having their growth be slower or later?