3 sessions of sclerotherapy and no results. What can I do?

By 3 sessions you should have seen some results.  I would not recommend, however, sessions closer than 6 weeks apart to give the solution time to work.  I have seen patients require as many as 5 sessions to resolve thier issues but there should be some improvemnt by the second session.  A vein light should be used for the treatment and if there has been no results then the concentration may need to be changed or a venous ultrasound may need to be repeated..  See a vein specialist.

It could take up to 2 months or more to see full results after spider vein treatment. If foam or liquid sclerotherapy is used, veins usually look worse before they look better. This should not be a concern for the patient because these changes are expected and also normal. It is recommended to stay out of direct sunlight for 3 to 4 weeks after the spider vein treatment or varicose vein treatment. At our vein centers, our specialists recommend to follow up at 6 weeks after treatment to reassess spider vein removal. Vein specialist also evaluates patients for chronic venous insufficiency before anything is done to make sure to not only take care of the cosmetic concern, but also treat the underlying cause of the superficial changes that are seen. All the best, 

What was the result of the Doppler standing? Was it done by a technologist or a doctor? Are they experienced on looking for sources of venous reflux? Is the Doctor Board Certified in Vein Disease?
The most common by far reason for poor results after sclerotherapy is the presence of venous reflux. The other option is that the concentration of the agent is too low. What medication agent are they using?
Sclerotherapy is a bit more complex than just been able to inject a vein...