I have a pituitary adenoma (16mm).My prolactin is 115, 3 (normal values 2, 8-29, 2ng/ml).I'm on thyroid medication. Probably have PCOS. Surgery or drugs?

Probably surgery. You probably need to see an endocrinologist or a neurosurgeon. If this gets too large it can affect your vision. They may recommend a trial of medication, but ultimately they will do a gamma knife.
Depends on the size. Prolactin level is irrelevant. You definitely do not need surgery if the adenoma is small, but if it is large and causes visual problems, then it needs to be taken out.