This is a fairly unusual problem, but not unheard of. Onions certainly do have compounds that when consumed, will get excreted in the urine and potentially change its smell. However, you should have to consume a significant number of onions before this would happen. The smell in your skin is also unusual. While you could certain sweat some of these same compounds out onto your skin, in the absence of sweating I doubt this would be the case. When you do eat onions the compounds that smell so strong do linger around in your mouth. I wander if you continue to smell them because you ate them and not because they are changing your urine or skin. You could verify this by asking someone that has not eaten any onions to smell you or your urine to see if they concur about the smell (as long as that isn't too awkward). The good news is that there are no diseases that I know of that cause your urine to smell like onions after you eat them. To be safe, you should schedule an appointment with your primary care doctor
to discuss the issue further. Your doctor can perform a simple in office urinalysis to make sure nothing is wrong with your urine.