This checks the basic system functions for infection and overall health. The number of red cells, the total number of white cells, the number of each type of white cell (who even knew there were 5 different kinds of white blood cells), the number of platelets, and the health of the red blood cells are calculated/counted. This can indicate (just for example) if the animal has cancer, what kind it has, if it is fighting an infection, if it is waging war with parasites, if it has a congenital defect, etc. It can also tell if it there are metabolic issues, (elevated protein in the blood plasma, etc) which can indicate if there are problems in the kidney or liver system.
This looks at specific blood chemical values (albumin, urea, sodium, potassium, lactate, creatinine) as well as enzyme levels (AST, CK, depending on which series of tests are run). These are needed in conjunction with the CBC results to look at key system function (again those kidneys and that liver).
These diseases (caused by parasites) can cause chronic pain and the symptoms you have described; I would imagine that there were probably elevated eosinophil values in the CBC (the White cell associated with inflammation, allergies, and parasite response) or they ran it because it is tick season (and the last 3 can be carried by ticks)
Sorry for rambling; figured I'd help clear some confusion up
