Wow, responses seem harsh for the forum. What got everyone into such a bad mood?
Yes, Amsoil is a great oil, and I don't think you over paid for oil since you have such long oil change intervals. However, you need to be checking your oil more often. What a lot of us on here do is we check the oil every time we stop for gas. This might be excessive though (hey, we're on a website dedicated to motor oil), but you should check your oil every 1k miles and if you find that it's burning oil quicker then that then you should check it more frequently .
What I do is I pull up to the pump, pop the hood and clean the dip stick. I don't immediately check the oil though, I lay the dip stick on some paper towels and fill up with gas. This gives the oil that was pulled up the dipstick tube time to drain back down so I can get an accurate reading. Once I'm done filling up, that's when I check the oil level.
If I was in your place, I'd do a full oil change to get back to a baseline and make sure everything is right. However, I wouldn't go back to Amsoil just yet. It's a great oil, but I'd first try to figure out what's going on with your vehicle before paying the cost of Amsoil, when it appears that oil is being consumed. Personally, I'd go with a high mileage oil, either Valvoline MaxLife (which is available in a synthetic if that's what you want), or Mobil 1 high mileage. Then start checking your oil every 1k miles or so, topping up as needed. Eventually you'll figure out what your consumption rate is, and then can decide what you want to do oil wise (go back to Amsoil, stick with a high mileage oil, etc).