I Have A Small, (I'd Say About .5 Cm) Lump

I have a small, (I'd say about .5 cm) lump on the left side of my right index finger just under the first joint. It is underneath the skin, feels like a bruise when pressure is applied to it and appears to be white. I do drum a lot so it could be from the stick constantly giving a lot of vibration and stress to the area, but I would like to be sure. It has been there for about 4-5 days of my knowledge.