I would just say that everyone is different, and some people do well on unusual combinations, but doctors put people on very dangerous meds all the time. All meds are very dangerous to some people, even if not to most. Some are very dangerous for everyone, but they're still used as the doctor doesn't know what else to do. Life is uncertain, medicine even more uncertain than most disciplines. Doctors use highly toxic substances on us all the time because that's the sate of medicine. The question is, does it work for a particular person? And another question is, does the provider know how to use the medicine and mitigate side effects and know how to use it most safely. That's again why I don't think general docs are the best ones to do this, as they generally don't understand the meds all that well. A good psychiatrist, if you communicate well with him or her, will recognize what's happening, but you have to find a good one -- most are hacks.
Cymbalta works similarly to Effexor, and is in the same class of drugs. I don't see how you could take both. It's also risky to take two antidepressants that target serotonin, as you can overdose on serotonin. I'm sticking with my opinion here that your doc doesn't seem well versed in this, pharmacists are well trained in how to fill a prescription but don't have experience with using them with a variety of people in real world situations as that's not what they do. This is what psychiatrists do every day, but you do need to see a good one.
You're probably not going to find a lot of people who take these two together because they're both highly stimulating antidepressants. My question is, why aren't you seeing an experienced psychiatrist instead of a general doc who has no special training in how to use these meds correctly and safely?