Boyfriend Has A Knot In Right Testical It Swells On

boyfriend has a knot in right testical it swells on occasion with much discomfort but it comes and goes seems as though it happens every couples of months for a couple of days then swelling and pain go away he has had a sonogram done and showed to b a knot or cyst and was suppose to have checked he has no sex drive and seems very tired all the time but we have no insurance for biopsy any ideas on a diagnosis?