There are a few considerations that you may want to consider as a holistic way to treat your pain.
First off, it sounds as if your physical therapist has covered some exercises for you, which will help to build strength if indeed, your arm are weak and a muscle imbalance is causing your pain. The way you perform the exercises is important, so an experienced trainer may be able to help you troubleshoot your form & adjust your other workout components appropriately
Muscle imbalances often stem from improper ergonomics at your workstation, at home, etc. It would be useful to get an ergonomic evaluation from an expert – many products that are marketed as ergonomic are not truly good fits for people.
For immediate relief, you could seek out various forms of manual therapy. Your PT would likely have a TENS unit, and could recommend a home version if it appeared to help with your pain. Someone else mentioned massage, but you may benefit from finding a person with specific experience in trigger point release, fascial stretch therapy, or strain/counterstrain therapy. The qualified practitioners for these types of treatments range from massage therapists, personal trainers, PTs, and occupational therapists, so depending on your area, you may have to search around a bit.
Are you currently practicing any stretch techniques? Sometimes, trying to power through a problem without proper rest can cause overly sore muscles, and therefore, more pain. You may want to explore some yoga/relaxation breathing practices to help aid your recovery.