Cymbalta is weaker than Effexor. Generally if Effexor doesn't work for some reason, Cymbalta probably won't either, it's usually a choice for people who can't tolerate the former. But perhaps you should try a higher dose of Effexor, 75mg is VERY low and I'm guessing that's why it doesn't seem to work anymore. You need a more substantial dose.
Because, personally I'd stay away from Cymbalta if you value your liver. It can do awful stuff. "Hepatitis that may progress to cirrhosis" sounds like a really pleasant side effect... not a really common one but it's indicative of liver toxicity. So is that fact that jaundice is a potential side effect. Oh, and a case of somebody dying from liver FAILURE linked to Cymbalta was reported post-marketing.
Maybe it's just me because my liver isn't in the greatest shape to begin with, but when you're taking medication, your liver is absolutely invaluable but often susceptible to damage. It's also usually critical to the proper function of the medications. I'd be concerned with making sure I protect it. Nardil is another antidepressant that's not particularly nice on the liver but Cymbalta really takes the cake, and many experts believe that it shouldn't even have a place in a psychiatrist's pharmacologic toolbelt because there are more similar and much more effective drugs on the market that AREN'T so hepatotoxic. It's filling a need that isn't really there... well, except for Big Pharma's bottom line.
If you want to try an *ahem* real SNRI, the tricyclics can be great and, while not perfect in terms of side effects, I can tell you I tolerated it MUCH better than (Side-)Effexor.
But probably the best idea is to try Effexr again, with at LEAST double the dose, and probably take it with Remeron as well, just by looking at the way they bind to each receptor, it's clear the two drugs have synergy. You get SNRI action and hit like a dozen receptors in *just* the right way. Remeron also indirectly increases activity at the 5HT1A receptor, generally the MAIN target of many if not most antidepressants, and so should enhance Effexor's 5HT1A agonism. 5HT1A increases the release of dopamine, so with these 2 drugs combined, you should get decent dopamine effects as well.
There is a very good reason they call this drug combination "California Rocket Fuel!" It does just about everything, even sigma-1 agonism which I can find preliminary studies about being just another one of Effexor's effects.