So unless your problem is related to a serious health condition, like diabetes or neuropathy (which your blood and MRI test results will rule out), it will be down to one, or both of these things:
1. Poor circulation as result of excess weight
I don't think this needs much explanation, but the more weight you're carrying; the worse your circulation is; the less blood-flow you're getting to the "rod", and subsequently the less impressive your "scaffolding" and ability to maintain said "scaffolding" is going to be.
To remedy this, do a lot of cardiovascular exercise; eat less than your burning off; reduce your total body fat; your circulation will improve and you'll see an increase in "inflation" (the good kind). You could also add L-Carnitine to your list of supplements, as it increases blood flow to the "rod", and it's completely natural, therefore won't come with any of the potentially nasty side effects drugs like Viagra or Cialis etc. do.
2. Chemical imbalance of Dopamine
So basically your brain is maxed out and has become desensitized to sexual stimuli. This is what I was trying to explain to you and some others in this thread:
Tinnitus and Sex Life? | Tinnitus Talk Support Forum.
Again, I don't know how often you watch
the pr0n, but it has a major effect on the male brain's ability to initiate and maintain arousal (there's even an official name for the condition called PIED or "Porn Induced Erectile Dysfunction"). So if you are watching pr0n, you need to stop, and start considering it an
impotence inducing drug. And this doesn't just go for pr0n (btw), you can replicate the effects of PIED just through too much self-pleasure (and mutual pleasure too).
I don't want to go too deeply into it, but while the
NOFAP community is based on a growing body of science, this idea of "numbing yourself to pleasure" actually predates any western science, as it's essentially the foundation of concepts like "tantric sex", and has it's roots in spiritual beliefs that encompass the idea of a "sexual energy" (such as Buddhism). But it doesn't matter if you prefer to look at it from a scientific or a spiritual perspective, because in both fields they're on the same page in as much as "sexual energy" or "dopamine", is like water pouring into a glass you need to let fully refill,
before you can drink from again and quench your thirst.
Anyway, maybe I went a bit too deeply into it there (like I said I wouldn't). So to cut a long explanation short, what I would suggest in your case: is a complete abstinence from sexual activity for as long as you can endure (maybe a month?), before you'll inevitably begin to start to feel your libido returning.
Personally, the longest I've ever gone is 3 months, and by the end of that, I was so switched on, I would have made love to a pineapple if I had been left on my own with it for five minutes.