Family history of depression=10% chance of depression. side effect of valtrex (valacyclovir)=7% of the same. assume 17% chance of depression if i take valtrex (valacyclovir)?

No: One can only make such an assumption if one has certainty that his chances depression in his PERSONAL case is indeed those numbers (very hard to prove), and also that such numbers would be additive. Thus, one cannot make such assumptions... it's too much of a generalization. Realize that even if there is a 10% risk, you may actually be a member of the other 90% who never get the affliction.