We can't tell you how you're getting punctures until you figure out where the tube's getting punctured. Is it along the outside of the tube, facing the tire? If so, there may be a sharp object that's worked its way into the tire. (Small wire shards from steel-belted car tires are a common culprit.) Is the hole along the inside of the tube, facing the rim? Maybe there's a problem with your rim tape or there's a burr on the rim. Is it at the valve stem?

Seems like it might be time for the ol' water test. Remove the tube, inflate it so it's about double its normal size, then submerge it in water. Wherever air is escaping, you'll see bubbles. The faster the leak, the faster it'll be bubbling.

As an aid to help find the source of punctures, many of us install our tires such that the maker's logo on the sidewall is lined up with the valve stem. When we get a flat and find the hole in the tube, we know how the tire and tube were situated relative to one another, so we can easily find the hole in the tire without having to check its entire circumference.