Welcome to HCM
We understand your concerns
You are very good at your description of your problem. You seem to be disciplined and perfect. You can find lot of bumps and blotches all over human body due to so many reasons, like boils
, warts, keloids
etc. All these pains little if pressed and they feel tender. If we start worrying for all these simple things, then there is no end to worrying. Please keep this in mind.
As you are not a doctor, it is always better to leave the diagnosis part to a doctor and to take his advice and don't worry about apprehensive thoughts.
The bump might be simple abscess formed after belly button inside sweating and unhygieninc practices. We seldom cleans inside belly button.If still in doubt, please consult a GP but no worry.