Pristiq (desvenlafaxine) 50mg taking it before bed as it makes me so tired, can't take it in morning. wake up still so tired! should i take it earlier in the night?

Not sure: Desvenlafaxine has a plasma 1/2-life of about 11 hr, so a single dose isn't mostly eliminated for 48-60 hr. However, side effects aren't necessarily dose- or time-dependent. Sometimes it takes up to a month for some side effects to become tolerable. The doc who prescribed it is obligated to work with you on this and should be willing to anyway if (s)he's a caring practitioner.