How to know if the heavy bleeding is due to intramural fibroids (2.2x1.9, 1x1) or dub? Dr says dub;can small intramural fibroids cause heavy bleeding?

Msybe. Fibroids ccan be the cause but hormonal irregularities can also be the culprit. It may be some combination of the two. You have to rule out an abnormal growth in the uterine lining. Speak with your doc.
Possibly, likely no. Small intramural fibroids are not likely to cause heavy bleeding. You can see this with small submucosal fibroids which are along the uterine lining. Most likely this is incidental, although one other option is that there are other fibroids the ultrasound (assumed that's where info came from) missed. I would suggest pelvic MRI to be sure. Ultrasound significantly underestimates fibroid burden.