It typically takes a few weeks to a month for an antidepressant to build up in your system and have an effect. The initial "feeling better" could be a placebo reaction, which is completely normal. For Wellbutrin specifically there is a chance when you first start taking it that depression, anxiety and suicidal thought will increase before it starts to work. I think you should definitely call your perscribing doctor and tell them what a rough weekend you've had - don't keep them in the dark as to how you are doing.

I just started Wellbutrin too (I'm on a couple others as well), so I've been reading up on it! Keep us posted as to how you're doing too, maybe we can compare notes

Best of luck.