Hello,
The kind of bump it is depends on whether it is present inside the testicles or on the skin. If it is present inside the testicles, then it can be an epididymal cyst or benign testicular growth. Even testicular malignancy cannot be ruled out unless proved otherwise. If it is present on skin, then it can be an infected hair follicle or sebaceous cyst.
An ultrasound testes can help in confirming a diagnosis. I would suggest you to consult a urologist and get it done. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
When your not sure its always a good idea to book an appointment with a urologist to "be" sure. Dont worry just take care of it and then rest easy.