Why do I have burning sensation while urinating?

There are numerous reasons for a penis to not stay hard as for instance stress, anxiety, physiological issues such as diabetes or hypertension, and some drugs. It's crucial to see the urologist or sex specialist, if this problem persists. They can examine your individual condition and tailor the proper treatment plan.
 

Since you are worried, it is suggested that urologist should be consulted for a detailed diagnosis and treatment plan. It could also be a birth defect, hormonal dissonance or some other medical comorbidity that causes the condition. Thus, one should consult a specialist in the field.

It requires immediate visitation to a urologist. The cause of the disease may be injury, infection or testicular cancer. This underlying cause needs to be diagnosed by a medical practitioner 

Urinary tract infections are often accompanied by symptoms such as a burning sensation when urinating, a need to urinate more frequently, and cloudy urine. These infections, regularly attributed to bacteria that penetrate the urinary system, are the ones that appear to be normal. To get the pain out, make sure to drink more water so that you can bathe the bacteria. OTC aspirin may bring you comfort. It is however very imperative to see a urologist for a proper diagnosis, maybe an antibiotic if needed. They can give you the right plan and the best course of action to get you back. 

Since your symptoms, it is possible that you have UTI or STI. For proper diagnosis and treatment of the situation, it is advisable to see a urologist or an STD specialist. Medical treatment must be sought immediately to prevent additional difficulties.