I had a pelvic ultrasound that says "there are non mobile non vascular echogenic foci with some reverberation artefacts in the fundal endometrium" ?

Hard to interpret: If you're not having any symptoms then this is not something I would worry about. It sounds like potential calcifications, which are likely benign. In general cancers present as thickened endometrium with vascularity. Fibroids have a more round and uniform apperance and polyps are more vascular. If these are small then that would be reassuring, but still continue follow up with your GYN.