You need to consult a urologist who would advise you the following investigations;
1) Testosterone levels
2) LH estimation
3) Thyroid function tests
4) duplex ultrasonography
5) Ultrasonography of testes
7) penile nerve test,
8) snap and strain gauge test,
9) penile biothesiometry.
Your present medications may also be the culprit for it.
The treatment would entail;
1) Selective PDE5 inhibitors are safe and effective (sildenafil, vardenafil, and tadalafil). So this is not only the first line but one of the best. The other things which can help are;
2) Vacuum Devices for Inducing Erection
3) Intraurethral Therapies
4) Intracavernosal Injection of Vasoactive Agents; people can be taught to give the injection.
If the above fail, penile prosthesis surgery can be tried, which has satisfactory results.
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