I think exercise is what you need more than anything else. Try going to the gym every day for the next 2 weeks, including at least 30min of cardio each visit. If you're still depressed and unmotivated after 2 weeks, read below.
Dopamine is the currency of the reward pathway. But it's also used in a lot of other neural pathways, most of which have nothing to do with feelings of wellbeing, and some of which are even perceived as unpleasant when they're activated. The dopamine system is extremely resilient. If you stop using drugs that mess with the reward pathway (if you do), and are healthy with your eating and sleeping, it should be back to normal functioning in a matter of months.
As a last resort, NMDA receptor antagonists upregulate dopamine receptors. They are not really safe drugs, and have significant mental and physical side effects and loads of drug-drug interactions. As I mentioned before, they upregulate ALL dopamine receptors, not just the ones in your reward and pleasure pathways. Without knowing anything about your past medical and psychiatric history, including the drugs (medical and recreational) and supplements you're on, I can't in good conscience recommend this route.
