Hello and welcome Jessica.

Following are the possibilites (since cardiac cause is ruled out);

1) Pinched nerves in neck
2) Myofascial pain syndrome
3) Costochondritis.

Pinched nerves can be due to;

a) disc disease in neck.
b) degenerative arthritis in neck.

Physical therapy, neck traction and neck brace are the mainstay of the treatment.

Myofascial pain syndrome is another possibility. These are hyperirritable tender spots in palpable tense bands of skeletal muscle that refer pain. This can be associated with degenerative disc disease in neck causing pinched nerves. Trigger points may develop after an initial injury to muscle fibers. This injury may be a noticeable traumatic event or repetitive microtrauma to the muscles. The trigger point causes pain and stress in the muscle or muscle fiber. As the stress increases, the muscles become fatigued and more susceptible to activation of additional trigger points. The treatment is following;

1) passive stretching of the affected muscle after application of sprayed vapocoolant.

2) physical therapy; simple muscle stretch, augmented muscle stretch, post-isometric relaxation.

3) deep electrotherapy; iontophoresis, phonophoresis, short wave diathermy, electrical stimulation, high voltage galvanic stimulation, biofeedback.

4) local analgesic patch / ointment / spray

5) anti-inflammatory analgesics; Ibuprofen (Motrin / Advil)

6) ischemic compression therapy; pressure on the points

7) massage

8) steroid shots

9) acupuncture

http://www.mayoclinic.com/health/costochondritis/DS00626

I would be happy to assist you further, if you need any more information.

You are very welcome.