The other two target other neurotransmitters along with serotonin. The possible danger is getting serotonin syndrome, which is an
overdose basically of serotonin. It's not common to get it, but when you start combining meds the way you are, you also combine side effects and if you combine meds that work on the same neurotransmitter it is possible to cause serotonin syndrome, or even if you don't, too many side effects of going after the same mechanism in the brain.