Strong smelling urine usually indicates an infection. It is important to go to your doctor and have them test your urine when you are experiencing the strong odor. Sometimes you might feel burning or pain when urinating if in fact it is an infection. The doctor can test your urine and determine whether or not it is an infection. Strong dark urine is also a symptom of dehydration if you are not drinking enough. Either way when you have the symptoms it is very important to get it checked out. I hope this helps
I am pretty sure that if it were a STD it would not just give you symptoms after sex. It might just be that you notice it more then. I think that you should go to the doctor and have your urine tested for a possible infection.