I don't recall that you mentioned this in your previous post about a burning sensation on both sides in the underarm area. Have you made an appointment concerning your previous problem? If not then I suggest that you also bring up the "heaviness" you describe here. There really aren't any definite answers here ... it takes a visual and hands on examination to diagnose any problem. Please see your Physician to put your mind at ease about these various concerns. Regards ....
There is no such thing as a nervous nut! Any changes we notice in our bodies brings on concern. Have you seen your doctor lately? I would schedule a check-up to discuss the area of concern. I don't know your age, but increased breast awareness, especially at the front of the breasts, could be caused by high estrogen levels, such as seen when hormones fluctuate in perimenopause or over the monthly cycle; chest heaviness could be caused by all sorts of things from cardiac issues to muscle spasms.
We wish you all the best -- let us know how your MD appointment goes!