It is a little difficult to come up with an exact diagnosis from what you describe, but, in general, a build up of pressure is often an indication of increased inflammation. That increased inflammation can be an infection or it may not. Of course, I don't know what postoperative medications you were prescribed or what instructions you were given, but if you have not been doing frequent warm salt water rinses, it is important to start them now. The warm salt water rinses causes the body to release built up fluids from either an infection or just inflammation.
So my suggestion is to use warm salt water rinses for 5 minutes 4-5 times a day. Place no heat or cold
to the outside of your face. If after about a day you still have the same pressure, I suggest that you get back to the surgeon. If you have not been on antibiotics and the pressure continues then that should also, most likely, be prescribed.
I hope the frequent rinses release the pressure and you feel better soon.