Cause of bizarre tooth pain when eating soft foods?

I've been feeling pain in my three upper right rearmost molars while drinking and eating soft foods. Cool water is enough to cause sharp pain in these teeth. I can bite down on meats, nuts and other tough or hard foods with these teeth just fine, but chewing SOFT foods like bananas or fig newtons has started causing severe, almost preoccupying pain in these teeth. This started just after finishing a multi-year invisalign treatment 2 weeks ago - I was given a set of very tight retainers.