I have been on metformin for 2 years. my doctor started me on januvia (sitagliptin) once a day. my blood sugar is 87 and i feel shaky. is it ok?

Yes: While 87 is probably lower than you are used to, it isn't a dangerously low blood sugar level & this proves the januvia (sitagliptin) is working. A small snack with complex carbs & protein, like a slice of whole wheat bread with some peanut butter, will make you feel better, and as your body adjusts to the lower levels these problems will go away.

Agree with Dr. S: The only caution to Dr. S's suggestion I would add is that you ought to be careful about how much you eat as you are at risk of gaining weight and worsening your diabetes. For nutrition: http://www.choosemyplate.gov/.