Do you take a short acting or long acting insulin?
I remember I used to have to mix Novolog
(clear - short acting) and Novolin (cloudy - long acting) when I was first diagnosed. But over time, I had to take Lantus, a 24 hour insulin, and then shoot Novolog, a short acting insulin, every single time I had to eat!
You just might need to change up your insulin routine or switch insulin types.
You body can build up an immunity and/or not respond to a certain type of insulin.