No, you're not alone. I had similar thoughts too, but more like: "why doesn't God just take me if I serve no purpose?" Over time, the frequency of asking this question has lessened because every now and then something happens to show me my life does serve a purpose. For example, I took fruit to a sick relative some days ago. It turned out it was one of his favourite fruits, and he enjoyed it. Simple, but powerful reminder to self that being in this world does make a difference in someone's life. I'm sure you've done countless things (some you probably don't even think of as significant) that have positively affected someone.