Lump in Pelvis Area

My husband is 32 years old and has noticed a lump on the left side of his lower pelvis for the past 4 yrs. It only shows up when he's been standing for long periods of time or general physical activity. It is not soft and it does not 'pop' all the way back in the way a hernia would. It hurts dully in generally, but when he has to urinate he describes it as being a sharp pain. It didn't used to bother him, but has complained about it more lately. Also, when he pushes it back in, sometimes it 'gurgles' - But not in an intestinal way. Like it's pushing fluid or a bubble around.There is no discoloration and it is very hard. It has no particular shape to it and it evetually goes away with rest. Could this be something benign like a cyst? What could be associated with it? Could it be serious? What sort of specialist would be ideal for this?

[AnnieBrooke]

Have him start with his normal internal-medicine doctor (his GP).  That doc will either know what it is or recommend a specialist.