It is not clear why you got a venogram before or after sclerotherapy. If you have had a DVT, it is likely that you have deep venous insufficiency (versus superficial vein insufficiency) or both deep and superficial venous insufficiecy. You also have post thrombotic syndrome. I would recommend that you wear stockings 365 days a year, rain or shine !
Sclerotherapy is the best done for tiny spider veins once the condition responsible for their formation, venous insufficiency, is eliminated. Under other circumstances, sclerotherapy is: 1. not effective, 2. in your situation, it is also not very safe, since once injected, the sclerosant solution is not controllable and its distribution, therefore, is unpredictable. It means, the solution can get into your deep system through so-called "preforators" and cause deep vein thrombosis. Right now, you should, therefore, check your deep veins in a specialized venous practice. The results of such evaluation will determine what needs to be done next. Hope it helps.