Don't know if you are still out there but to let you know, my wife, 52, had a similar dianosis, mucinous adenocarcinoma, unknown primary with mets to the brain. They were treated both surgicially and with Gamma Knife, followed by 30 days of whole brain radiation.
That was nearly 16 months ago and, except for a back ache caused by a fall caused by inbalance, a side effect of WB radiation she is in better health than before the diagnosis.
Moral: hang in there. You are young and strong and will do fine.