Hi and welcome to HCM. thanks for the query.
It may b eclot and in most cases it is treated by takong anticoagulants or heparine/clexane
. It can be svere if there is pain in arm
and difficulties in movements. If there is only heat then it can be beginning of thrombophlebitis
or it can pass spontaneously. At this point you should follow doctors recommendations and if some of these signs I ve mentione doccur,you need to visit doctor ASAP. Wish you good health. Regards