If you have a lot of funk in your crotch/groin area, particularly after sweating, it is probably not a basic hygene problem, but you likely have a serious fungal or bacterial issue. A fungal problem will often have a vinegar smell while a bacterial issue can range from standard B.O. to a wide range of unwelcome odors.

Either way, it is something you should promptly address and stay on top of. Liberal use of an anti-bacterial soap when showering will help. After showering, always use a fresh clean towel to dry the area completely. Then try a regimen of 3 - 5 days with a quality anti-fungal powder (I have found a spray-on jock-itch powder works best for me) or a light application of anti-fungal cream. In a pinch, the ones for feet will get the job done, but an anti-fungal cream like those marketed for feminine itching should do the trick.

Once you get it beat, you will want to continue with the anti bacterial soap and use the anti-fungal powder at least once a week to keep it under control year-round. In situations where you know you will be under heavy exertion (hiking, heavy labor, etc..) , you may also want to apply a good antiperspirant to the affected area in advance.

Take care of it properly and the odor will subside, plus you'll feel much better.

I should note that if none of this works or if it becomes a recurring problem even after following these steps, you really should see a doctor as you may need some sort of pills to keep it under control.