FS is known for being on the high side of the calorie calculations, try calculator.net and see what it gives you
Personally I think its more important as to what you're eating. Are you hungry, are you eating enough nutritious foods to keep you healthy.
Its sounds like you have a good metabolism and if you're not losing weight at that intake and are maintaining then why is it necessary to go up to some number computed by a program that doesn't really know you.
If you really want to up your intake then log your food in daily. Slowly add in some healthy choices to bring your calorie count up slowly and see how your body reacts to what you ate.
There is so much more to this question and without knowing your health and age and history, it's hard for anyone to give you detailed advice.
I would go slowly and see how you respond to the added food, say 100 cals at a time and go from there.
If it is a plant, eat it, if it comes from a plant, don't!