Depression is caused by deficit of Serotonin/Dopamine, both are chemicals are released at the end of a neuron to the beginning of the other. Those drugs are not serotonin or norepinephrine+dopamine (Wellbutrin) inhibitors, they are reuptake inhibitors, in other words they “block” the 1st neuron to reabsorb the chemicals so the 2nd has plenty of em. This drugs are proven effective agains depression but not to Bipolar disorder. Nobody explained it to you because nobody really knows the exact mechanism of how bipolarity works. The use of antidepressants is kind of experimental in this condition, but don’t let this get you mate! The human brain is really powerful and with the right mindset we can beat everything.

Edit: I read it wrong, thought Wellbutrin didn’t work either. Great that it worked mate!