Flat tires

About three weeks ago Amber, my roommate had a flat tire and got it fixed. Well, it is still going flat and she has had it fixed three times now. It is flat again, so she is just going to get an all new tire this time. Anyhow, it is kinda suspicious now because in the matter of a month, AMber had a flat, Aaron(Ryan's roommate) had a flat, I had one and now Ryan's is flat today. Is it just that much construction around with that many nails? Or do we have more of a problem with someone personally? No matter which one it is...it really sucks having to fix or change a tire once every week!