Well, first of all, you don't have to do what a doctor recommends. You can say no. Once you start the medications, depending on how long you've been on them, it's not that easy to just stop them, but you can if you want if you've only been taking them a very short time. I'm assuming you also suffer from anxiety, though you don't say so, otherwise the Xanax would make no sense. Topamax isn't approved by the FDA for depression treatment, but some studies do show it can help some (and as with any other drug affecting brain neurotransmitters, some are made worse and more anxious, but that can happen with Lexapro as well). Once a drug is approved, docs are allowed to use it for unapproved purposes. It's main effect is on GABA, the same neurotransmitter targeted by your Xanax, which is a target of most drugs for epilepsy. Topamax is an epilepsy and migraine headache drug. So there is some evidence it might boost the effect of the Lexapro. However, let's start with the question, if you're tolerating the Lexapro well, you aren't actually at the recommended dosage for treating depression. You are at the recommended dosage for treating anxiety. 20 mg is the dosage the manufacturer originally recommended for depression, so the first question is, why not up the dosage of the drug you're on first and see if that works? It would be the least bothersome thing to do for you, as since you've been on Lexapro for awhile anyway it's going to have all the problems of stopping it anyway. A second question would be, why add two drugs instead of just adding one? If the topamax does the trick, why add the wellbutrin too? Why not wait and give the topamax a chance first? Wellbutrin is commonly paired with an SSRI such as Lexapro, though usually it's done to decrease the side effects of weight gain and sexual problems. If you're an anxiety sufferer as well, wellbutrin is perhaps the most stimulating of all antidepressants, so again, if you need Xanax, this might not be a first choice for you. Third, if the Lexapro was working and now isn't, that's another argument for increasing the dosage, as these drugs do poop out for many people. You can also just taper off the drug as slowly as you need to and try something else altogether -- if a drug isn't working at all well, there's no reason to add another drug to it, you stop it and try a different drug. This isn't to say your psychiatrist doesn't have reasons for doing this, but it does address your fear that you're being over-drugged. You very well might be. It all depends on you. Some people have problems so resistant to medication there's no option but to try things you wouldn't do otherwise. But given the little you've said so far and given the low dose of Lexapro you're on, I'd want to question my psychiatrist pretty deeply to make sure she knows what she's doing -- just having a degree doesn't make that so -- and you might also want a second opinion just to make sure this sounds right.
Try it and see what happens.
Right now we want to get you out of that depression, so trying different meds hopefully one will work.
After the depression lifts, then you can work on adjusting the meds, possibly trying decreasing one, and if you stay out of depression, decreasing it more, until it's determined you don't need it.
With the new meds, if one of them causes a bad side effect, let the doctor know. On rare occasions I have stopped a new med after a few days when it became obvious it was causing bad side effects. I let my doctor know.
Otherwise, hang in there. It does get better. But it sometimes takes a long time. Best wishes1