Is there a way to enter breastfeeding?

If you mean logging your breastfeeding for the purpose of stats, then you could create a custom acitivity, name it Breastfeeding, and start/stop it in the same way as any standard sport activity. You would then see it in the Calendar, as well as in the list of activities.

Ah, OK, in that case you could do it by editing the Calories manually in the custom activity, or you can do it also through MyFitnessPal:

https://support.myfitnesspal.com/hc/en-us/articles/360032623451-If-I-am-breastfeeding-or-nursing-how-do-I-adjust-my-goals-

Thanks!