Pelvic ultrasound states "no discrete myoma is identified". What does this mean? Do they mean there is an obvious one but they aren't telling me?

No fibroids are seen. Basically that phrase tells me that the reading doctor did not find a fibroid, but that there probably was some heterogeneity or shadowing on the scan that makes it hard to say definitively that there are no fibroids (myomata) at all.
No obvious fibroids. Uterine fibroids typically present as focal masses along uterine wall/muscles. What the phrase says is that you don't have this type of fibroids. Rarely, however, fibroids can be so small and diffuse and replace the entire normal uterine tissues that these fibroids cannot be individually visible on ultrasound. This is so rare that it is unlikely that you have this but nothing is 100% certain.