I have really bad night sweats i wake up soaked i take effexor (venlafaxine) is this the cause?

Yes: Yes that can be a side effect when taking effexor (venlafaxine).

Sweating/diaphoresis: may affect up to 22% of patients who take antidepressants. Options include stopping, decreasing, or changing antidepressants. If your medication is effective then prescriber may consider adding benztropine 0.5-1 mg a day or aripiprazole (augments antidepressant and may reduce sweating). Combining these meds with venlafaxine may increase dizziness, drowsiness. Best regards for relief.