Of course you should drink plenty of water, particularly in such situations. It may be due to so many medicines you are taking. If you could list the drugs, I would be able to analyse some more. How ever, Amoxicillin
and Doxy do not normally cause such symptoms.
I think, they will disappear, within few days. Or else visit your physician for rechecking the drug combinitions.
Hope I am clear.
All the best.