I would imagine that the force feeding attempts could stress him out to the point where he won't eat. Most people only force feed a hatchling that has never eaten anything. I'd try a live rat pup with the eyes still closed and keep it in overnight. You should post a photo of your setup and the snake. Not sure you should be force feeding a three month old snake. Personally I wouldn't use a live mouse unless supervised at all times. I find that if the snake strikes the mouse and misses the mouse figures it out and becomes aggressive towards the snake and can do some serious damage. Usually I watch the live mouse and if the snake misses even once I remove the mouse and gas him with CO2 and try to feed fresh kill, then pop it in the freezer if the snake doesn't eat it. Once the mouse figures it out you should never use that mouse again to feed live. Rat pups are totally harmless as long as their eyes aren't open.