It can take anywhere from 4-6 weeks for it to be completely working, though you may notice some things sooner. Such as being able to think clearer and your energy level may go up. So give it time and be patient.
I wish you luck with the wellbutrin. I use to take it but take effexor now.
Your doctor may increase your dose too if you don't notice something by four weeks.
Take care and keep posting.
Are you new to this forum? If so, welcome. You will find there are a lot of kind and caring people here who are always willing to listen.