Do not worry too much.
You may be what Doctors call "slow".
I'm like you and my follicles grow from CD18 to CD20 from 13 to 22 mm.
This was a natural cycle with no meds.
When I did IVF in january 2007 all the docs said I was slow ,I was so discouraged...Turned out I had 35 eggs retrieval day...Unfortunately it ended in ectopic but that is another story.
Stay positive!
Miky
If I understand the abbreviations correctly, CD 17 would mean you're taking Clomid? I'm not sure if this will help at all b/c when I took Clomid it didn't do a darn thing for me (although it has helped MANY), however I do use injectable meds to make my body ovulate. Just like when using clomid, I had to go in for many bloodtests and ultrasounds to monitor those follicles. On my last attempt, it took forever for the darn things to start growing! It seemed very slow at first but in the last 2-3 days it jumped from 15mm to 20mm. I'd say that if the nurse seems to be ok with the numbers, I'd try to be ok with the numbers (not to say you can't research and ask... heck, that's what I do).
Best of luck to you!