The first thing that comes to mind is prostatitis (or other infection). It can cause back pain, leg pain, pelvic floor pain, difficult/painful urination, and of course pain during intimacy. It is painful, all the way around, in areas both near and far. There is usually significant internal inflammation.
Prostatitis needs to be treated consistently for a lengthy period of time, and treatment should include (natural/herbal) antibiotics or anti-virals, dietary changes, nutrition and supplements to address specific symptoms, as well as physical medicine (frequent warm sitz baths, massage of the prostate gland, frequent times of intimacy with eja*****ion, etc).
The second possibility is chronic pelvic pain caused by a persistent contraction of the pelvic floor muscles. Kind of like a forever charley horse, except in the pelvic floor. One treatment involves releasing trigger points. This is closely tied to stress, and worsened by stress. I believe chronic pelvic pain is a multi-faceted ailment, and should be treated by several different modalities (allergies, chiropractic/massage, nutrition, natural medicine, stress management, etc).
None of the treatments are especially pleasant, but...
I am sure there are other possibilities, some quite serious. Please ask your dh to get a clear diagnosis (exam, blood work, urine, PSA, etc), or at least rule out some things. I would not delay, nor would I begin conventional medical treatment without a considerable amount of prayer and research. Once you have that you can examine the treatment options.
Herbs can be a great part of treating male reproductive health, but you need to know what you are treating in order to select the right herbs (and vitamins, minerals, diet, etc).
Be encouraged. You can be a wonderful help to your husband through this.