Jen, count your blessings, and keep track of what she is doing - that's one of the ways you'll know if she is sick.
I too had this question, only when my DS was 4 or 5 months. The doc said count your blessings and enjoy the respite from the messy diapers!
She is just digesting most of what she takes in, which is good for her, and you get the diaper-less dividend! Her body is able to make the most of your milk (when you start even water, it goes back to being more frequent, though not absolutely.)
DS is now on 2 meals of fruit/veggies and oatmeal a day, and he sometimes skips a day, sometimes has 2 a day. So that isn't so bad, either.
Good luck! and Good for you, questioning! :)
M.
PS: she isn't constipated! Just don't worry about what you're not seeing. She is constipated (if the doc didn't tell you yet) if it is hard or like a stiff paste (has shape).
Thermometer will do the trick, but generally, just wait for it. She'll do fine. So will you!