I've had a pain behind my shoulder blade and a tingly numb pain going down my arm.i know i have a pinched nerve, and elevated cholesterol. heart attack?

Probably not: At your age a heart attack is generally unlikely especially if you have another explanation for your symptoms (pinched nerve) but either way you should see your doctor to sort it out and maybe a neurologist if it turns out to be nerve pain.

You sound worried: You are most likely on right track regarding nerve compression, and this may be within neck or in shoulder area, a thoracic outlet issue. You would benefit from seeing a neurologist, getting images of neck and maybe electrodiagnostic study, and likely conservative feldenkreis therapy or motorized cervical traction will reverse symptoms.

Likely nerve: You are young, and based on your described pain pattern you possibly have a C7 radiculopathy, less likely heart attack. For radiculopathy, it is wise to first try non-surgical management and if symptoms are intractable and progressive, i would consider seeing a neurosurgeon.

Pinched Nerve: It is most likely a damaged nerve in your neck however this answer should not substitute for a thorough evaluation by your doctor.