Hi! I Play Tennis And After Some Very Long Matches

Hi! I play tennis and after some very long matches I noticed pain and knots in my tricep. It also sent pain to my elbow which gets better with rest. In trying to rest several weeks I also feel similar in my left (non-dominant) arm. Could it also bedroom iPhone use?

An airrosti provider suggested aconeus/tricep tendinitis? Even after treatment, rest and massages I still feel knots in triceps.

Help! Any suggestions for treatment?