If the snake is not getting bigger then you probably are not assist/force feeding it often enough. After each meal is excreted (brown, not urates) I offer the snake a live hopper mouse. If the snake denies the offered food: I will assist feed 2 or 3 pinky mice. I repeat this cycle over and over again (excluding shedding times) until the snake learns that it is time to eat when the mouse is shown. It usually doesn't take mine more than a few weeks to learn-they all seem to get the message eventually. So far I've had 100% success (with dozens of non-eaters).

Note: Some of my hatchlings will even try to regurge after assist/force feeding-In this event-I have to pinch my fingers above their throat and massage the prey item down into their abdomen. This takes a while and if I have 10+ non-eaters I will be dropping F-Bombs like its WWIII by the end of the session.