Herceptin side effects?

I have been on Herceptin for 14 months since diagnosed with liver mets. Chemo (taxotere) stopped June 2003. CAT scan in January 2004 showed liver mets had disappeared and doctor said I was in remission. I am suddenly not doing well at all. Off balance (fell twice), very weak legs (couldn't get out of bathtub, trouble walking), dizzy, headaches (for about two months now). Anyone know if these symptoms might be from Herceptin? Oncologist says not from Herceptin and he does not believe it is brain mets but did not order a scan as he thought it might be other drugs (I take Celexa for depression and a tiny dose of Klonopin at night to sleep). Anyone have any thoughts or ideas of what I should do?