When should I do follow-up tests after being treated for thrombosis and can thrombosis occur while using Vessel Due F?

I am after being cured of intramancular vein thrombosis of the right leg. Neoparin finished injecting at the beginning of March and since then I have been taking vessel due 2× 1. After a period of two weeks, my leg began to hurt again. The doppler test did not show thrombosis in this leg, and on the contrary, everything is fine. If the pain persists, sometimes weaker, sometimes stronger, should I repeat the test from time to time? If so, how often should I do this? Can thrombosis occur while taking vessel due? I did not have a follow-up visit to the angiologist until mid-May.