HI,Good Evening.Thanks for your query.I studied the query in-depth.I understand your concerns.
I need to have more info-which I can get after clinical examn only.With whatever facts told in your query,I would try to give most probable causes to help you to reduce your worry.I would advise Excision
Biopsy which would fix the diagnosis.
-By your description,its mostly of subcutaneous lump and you should relax on that positive ground.
-Mostly in my opinion that lump is -Lipoma/ fibromyoma-as lump is painless.
-Excision Biopsy-would fix the differrentiation of the causes of the forearm lump and would treat them as well.
-You need not worry of the outcome as both these tumours are benign.Littlle variation in size should not worry you,unless its painful and with regional node enlargment.
-Hope this would help to regain the lost-health fast.
-Wishing you early recovery and good health.