What would cause 3 marble sized lumps in a male's groin area?

Inguinal lymph nodes: Most guys have a few, especially if they go barefoot outside. If they're really big or are fixed to the surrounding structures, they might be worth having your physician see them.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.