Paul, I don't believe there is a "normal" dosage of Wellbutrin. I started with 100 and was quickly put to 150mg, which is what I currently take. I think it all depends on what you and your health team decide works best. Have you tried taking a combination? I take Zoloft also and I feel it works well.
If you look at the website of any drug manufacturer you will find recommended dosages as reflected in the studies they did to get FDA approval. You can also talk to a pharmacist or your psychiatrist. Now, some people absorb drugs really easily and will need less, some absorb them less well, and some won't absorb them at all. This might not be a drug that will work for you, it's trial and error. While drugs are often combined, you don't usually combine a drug that doesn't work with another drug. If it's working but just not as well as you hoped, combining drugs can be more effective, though it also comes with greater chance of side effects. When this drug is combined with an ssri as described above, it's usually to combat certain side effects of ssris, such as weight gain and sexual problems. You also don't say how long you've been on it -- it takes 4-6 weeks for the average person to notice benefits, though side effects will start right away and different people will experience different results. Also, most people don't find all their problem go away by taking medication -- it improves things, but doesn't cure them. Therapy might be a way to cure them, though there's no guarantee that will work, either.