You poor thing. My thoughts are with you. When I have an allergic reaction to something I have to take antihistamines for a few weeks afterwards because it takes a while for my body to settle back down again. If you are suddenly histamine sensitive it might be that they are keeping you on it long term which is usually ok as a lot number of people take zyrtec, claritin regularly. When my bloodpressure spiked from the midodrine it caused headaches, hotflashes, nauseau. If this has all been since you stopped eating carbs is it possible that maybe you aren't getting some nutrition from carbs that you needed? Hang in there and hopefully things will calm down soon.