Welcome to Health care magic.
1.Even if the lump is not sore, Not active in infection it could be at insertion point of the muscle, tendon.
2.So over a period it will cause that muscle, tendon,
nerve ending irritation and cause pain / discomfort.
3.In this case it could be
lipoma - fat containing lesion - According to your description.
4.Let it get examined and get a
ultrasound scan done - it will hep to find out the nature of the lesion its source and extensions.
5.After that you can plan for excision. ( if its causing discomfort and progression in growth) Good luck.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.