My Son Has Been On Paxil For One Year... We

My son has been on Paxil for one year...
We are switching him to Wellbutrin
He was taking 40 mg
And stopped last week after being weened off for about a month
For 2 days he has been having legs aches ( he explains ,, feels like growing pains)
Diarrhea , he threw up one day and headaches ...
He has staring taken Wellbutrin about 3 weeks ago along with the Paxil
That's what his dr said to do 40-30-20-10 then stopped
Could he be having withdrawals ? He has no fever - legs are killing him
Thank you so much for an answer
Michele Foristel