I have a hard time getting enough calories in too. What happens with me is, Im not hungry for 2-3 weeks, then that week before my period, Im loading up on higher calorie foods,(because Im starving) but still low carb. So it seems to even out for me.
But if this doesnt happen to you, adding calories can be done by adding, tbsp bacon bits, shredded parm or cheddar on your chicken, add mushrooms fried in butter.....or add ham slices and spinach to your scrambled eggs etc. Stuff like that.