Calm down!
After establishing your diet plan, your body will naturally adjust to urinating less often.
First off, the weather has been hot all over-are you sweating more?
Are you retaining water? Check your legs and ankles-are they feeling tight? Are your fingers stiff and do your rings fit normally? Is your period due?
Are you having any trouble breathing?
If you are peeing normally (but not copiously like you expect) you are probably fine.
If you have a full chemstick rather than ketostick-check and see what else you might be spilling in your urine-specifically blood and protein.
Lastly-I agree with the others. You should be concerned about drastically reduced urine output and call your doc ASAP.