That is very, very unusual.
I've not read of anyone experiencing those effects. Especially, at such a low level (2.5mg).
We got a Sheltie a couple of months ago, and they have a potential for MDR1 gene mutation which causes significant/serious attentuation to so called standard drugs.
I think it possible you have an extremely delicate neurotransmitter feedback system, which may explain why you've had so many problems finding something that works for you. I think no matter what you end up being Rx'd in the future, you should talk to your doctor and see if s/he will start you at the absolute lowest level possible.
Just came across another post regarding folate deficiency, or more accurately sub-standard folate sysnthesis to some other neuro related chemical that has been discovered. Do a search on here for Buspar and its in a link someone posted. Googling I found this quickly, which is from a Manf. I believe, but is good for general info. http://www.deplin.com/folate-for-depression/
For me, after a number of months on Buspar, I believe it worked modestly for what I think was short-term, possibly PTSD GAD. However as my work stress has leveled off, so has my stress, siginficantly.
I am going to try supplementing folic acid at 3-4mg/day for the next month or so to see if that helps any. I've always been easily frustrated, which I think is probably in someway intertwined in my stress/reaction.
I'm not sure if it helps at all but weight gain wasn't listed on the pamphlet I received from the pharmacy. It does seem to do a decent job at relaxing on a subconscious level, haha, I felt so zoned out and my muscles were completely relaxed.