Can an ecg change ?

I had one conducted about 3 months ago, due to pain in my chest, jaw, shoulder, arms. The results stated that everything was normal. My doctor diagnosed me with Anxiety.

Lately, iv been getting the same pain, kind of worse though, my chest and jaw hurt. My jaw hurts more than my chest. (I also have TMJ but haven't experienced any pain associated with that for a long time, since recently)
It happened about 2 weeks ago since today. The pain usually lasts a few seconds, the most maybe 40 seconds or so. It's sudden pain, it's not a "sharp" pain, more like a squeezing pain. Only on the left side of my chest. Happens about 5-7 times a day. Can this be Angina or anything similar to Angina? Or perhaps my anxiety?

Can an ECG result Change within 2-3 months?