Have your testosterone checked. It's an inexpensive blood test, can be done at the same time you do the next PSA (or sooner).
Google low testosterone to see the many debilitating effects a low T number creates, many of which are life-threatening. If you have clean PSA's you should have no problem getting your urologist to come up with some solution for you. If not, talk to your GP.
This is a good link to get started with:
Follow the leads in the article for more information. Ignore the pic of the 76 year old with the 33 year old girlfriend: It's too much work.
A lot of GP's are getting into anti-aging medecine. If you can find one who's into body building or cycling, he would be more sympathetic.
The most convenient route is the patch (which I used for two months to counter the effects of a Lupron shot prior to my RP), but of course it's also the most expensive. The cheapest (dirt cheap) is injection, using a needle like the one used for insulin, into the fat of your stomach. Not a problem unless you have needle phobia.
Testosterone is as tighly controlled as morphine because of the abuse, so you might have to twist an arm or two, or do some doctor shopping. Your GP might be more amenable than your urologist, the urologists all think that testosterone is the devil. You can explain that since you no longer have a prostate, you really don't have to worry about prostate cancer anymore. . . . but saying testosterone to a urologist is like pulling the string on one of those talking dolls.
Normal T is 300 to 1000, but the body builders like to see at least 1200 (or much higher). You want to be around 600 minimum, but here again, if you're at 400 you might have to twist some arms, since you're in the "normal" range.
Side effects are almost non-existent unless you abuse it. You'll sleep better, sleep less, have a lot more energy, and of course be a lot more interested in sex.
You want to take it initially in a fashion that will encourage your own body to step up to the plate and provide your own, if possible. That means 3 days on, 4 off, and so on. If you're on continuous T replacement, your body will shut down it's own T production (serious body builders live with shriveled nuts but very high T numbers). If you're lucky, the cycling will jumpstart your own body's natural T production.
DHEA will also help a lot, but it has to be taken in 200mg daily doses to really be effective. The standard 25MG is a waste of time. If you do go this route (200MG DHEA), you will also want to use an estrogen blocker, as a significant part of the free testosterone will be "aromatized" into estrogen. You need some estrogen to keep your brain elastic, but too much and you gain unwanted weight, especially around the breasts. Your local body builder oriented health store will point you in the right direction.
This is a highly condensed simplification of a very complex body interaction, so you may want to do a bit of research yourself to really understand how it all fits together. I have to say that I am not a medical doctor and can not give medical advice. The above is a (very brief) description of my own research and experience. This is a free site that goes into a lot of detail:
Good luck, and let us know how you make out.