3 miles a day might not sound like much, but think of it this way: you added half again (50%) as much milage in a one week period (2 + (.5)*2 ) = 3; the recommended guideline is 10% per week!
Try something like: 2 miles a day, with maybe 1-2 days in a week being 3. next week make it 2-3 days, and so on.