After donating plasma my teeth ache. is that normal?

Depends: It may be related to the drop in fluid volume...Depending on rate. Check with your doc if doesn't stop within a day or two.

It is not uncommon: It is probable due to a temperature change in your blood. Your roots are embedded in the gums and bone the nerves run out of the roots to supply blood to the teeth along with sensation. Thus the change in temperature can cause sensitive teeth.