This has nothing to do with the Tetracyclin stains.

Both dentists may be right, since the symptoms you described can be gum problem from the nerve or the other way. However, "现在几乎一半牙齿有松动" indicates that you have at least gum problems and the first step would be a consultation with a periodontist (ie gum specialist). You might need a second consultation with a endodontist (nerve specialist) based on your periodontist's diagnosis/treatment.

Good luck.