How can i stablize my weight?

I'm 28yo guy and I am 69kg (152lbs) with a height of 5'9 (180cm). I also a very avid jogger and like to run on most days. I really need to stabilize my weight otherwise I risk becoming underweight. I want to up my calories intake from an 1800 average to a 2500 but I am struggling. I have to force myself to eat this extra food and its horrible eating when you are full. Can someone suggest some healthy ways to get these extra kilojoules without force feeding myself?