I am writing this to you with great expectations. I am 60 years old and retired, my wife is 48 years and working. Last year she had to undergo an operation and got her uterus removed. After that her vagina opening became reduced. I am not able to put my penis in easily. She feels pain. I like to have sex very often and my size is quite big. I tried using butter, but that didn't help much. My wife does not like oral and anal sex. Please advise me what to do so that I can have happy sex life. 

If she had her uterus removed, they probably also removed her other organs so that she is no longer producing certain female hormones. That will lead to vaginal dryness. So it is not the size of her vagina that has changed, but her ability to produce lubrication. It is this lack of lubrication that is causing her the pain. Butter is not an acceptable substitute. You need to use a medically safe lubricant like KY jelly. I suggest you ask your pharmacist to recommend one, or even buy several different brands and see which one works best. I believe this will solve your problem.