The ONLY thing Viagra does is give you an erection. It is NOT a magic aphrodisiac. I don't know if you use cannabis, but for some people some strains of cannabis work as a sex-enhancer; it depends on the dose, strength, and the individual. For some people any kind of cannabis will put them in the mood, it's a suck-it-and-see thing.
You might try Tongkat Ali, it's got to be the real stuff to work but it's a temporary testosterone booster; for some men it gets them immediately very revved-up but you should really consult your doctor because although it's legal and organic, it's pretty potent stuff and it can cause flushing, heart palpitations, headaches, sinusitis, and eye strain (seeing blue spots is common). Continued use can cause hair loss. Tip: If you don't get any pleasant effects from a small dose, a larger dose won't be any better.
If cannabis works for you, that's what I would stick with, you can't go far wrong.