Hi agnas, welcome to the board!
No test for Lyme is completely reliable, and results can vary by lab. From what I understand, the ELISA only catches about 30% of Lyme cases. I believe it is significant that yours was positive in 2007. Which lab did your Western Blot? If it was a lab such a Quest, they do not list all the Lyme-specific bands. It is important to be tested by a Lyme reputable lab such as IgeneX in Palo Alto, CA.
Besides Lyme, ticks can transmit other infections including Babesiosis, two types of Ehrlichiosis (HME & HGE), Bartonella, and Mycoplasma. Many people who have Lyme are co-infected. It may affect treatment choice and progress. Have you been tested for these by a Lyme lab?
Three weeks of treatment is not long enough for Lyme even if your infection was caught within two weeks of the bite. I do not believe you have been treated properly. It is very important to see a Lyme knowledgeable doctor and be tested for the co-infections. If you need a recommendation, you can email me at firstname.lastname@example.org
It is also important to learn as much as possible. I recommend reading Dr. Joseph Burrascano's 2005 Diagnostic Hints and Treatment Guidelines For Lyme and Other Tick Borne Illnesses at http://www.ilads.org/burrascano_0905.html He is one of the top Lyme doctors in the country, and many Lyme doctors follow his protocols. I also recommend the books "Everything You Need To Know about Lyme Disease Second Edition" by Karen Vanderhoof-Forschner and "The Lyme Disease Solution" by Kenneth B. Singleton MD.
I hope you can get answers soon.