What Causes Pain In Shoulders Radiating To The Base Of Neck?

A few months ago, I 'hoisted' an extremely heavy, large suitcase off the ground and into the trunk of my car. And ever since then, I have pain in my left arm/shoulder and up into my lower neck area. Specifically, however, the worst of it is located lengthwise on the outside (closer to the inside than backside) of my arm.
I came to TX, after loading my car, and have been kept awake some nights, with pain. My friend had some prescription anti-inflammatory meds that I took a small portion of one/day for a few months, completely relieving the pain!
Now, however, I'm out of the meds and the pain is back. I've also tried massage myself and COLD on it, without success. And I've started taking one ibprofin each night before bed.
I'm extremely healthy and don't take ANYTHING, so don't like putting this in my body on a regular basis, to tax my liver, but the pain is bad enough to give in to it.
I DO have Medicare and a Medi-gap policy and am ready to give in and actually GO to a doctor!! What kind of specialist should I go see? Mostly, this feels like muscular (sprained tendons/ligaments?), but sometimes, it feels like joints/bones are affected, as well.
FYI, for years I had a cervical condition, for which I was treated a LOT, but for the past 4 years, I haven't had a recurring episode ... and I have a horror this could have consequences on my neck!
I presume that I'd need an MRI to see soft tissue, correct? And, of course, to eliminate possibilities of skeletal damage, I'd need Xrays.
Any suggestions you have would be appreciated!
Carolyn