My dog has cramps off and on making it difficult for him to lye down and rest....What could it be?

He is a Yellow Labrador Retriever; 5 years old; 90 lbs. He continues to be playful, active, runs up the stairs with no problem and is eating and pooping well. The past two days he has been randomly getting cramps which causes him to yelp in much pain. It makes it difficult for him to lye down and rest since it looks like this is when he gets the sharp pains. He licks the right hind leg after the pain comes in. We checked him for scars, abrasions, bumps. lumps but no sign of anything. This started just a couple of days ago. I'm on a tight budget and have no idea what it will cost to get him diagnosed; therefore, i was wondering if there is something i could do at home to provide him comfort or should i take him in? Any suggestions?