A superficial blood clot should not cause considerable pain under normal circumstances. Since your Doctors did not recommend Heparin, it seems the clot is of a small size. This also makes me wonder whether the pain is due to something else (form a joint or pinched nerve).
I would like to know some additional information from you : You can reply as a followup -
1. What were the symptoms to begin with (during the initial diagnosis ) ?
2. Are the symptoms similar now ?
3. Was a Doppler scan done, if so do you know where the findings ?
4. Do you have pain in any other joints ?
You can reply as a followup