New belts stretch, so they need re-tightening after a few weeks. Could be that wasn't tight enough in the first place if its only been on a few days. Try some silicone based spray on differnt areas to see if you can isolate the squeak.
Mine belts were only bad in cold weather so it could be the change in weather causing the issue. Tightening them sorted it out.
If your arms are thin enough you can reach the pulley tensioners by reaching down behind the radiator. If you can't get your arm down there then you need to get under the car. 5min job if you don't have to get under the car probably half an hour if you do.
If you go behind the radiator, look at pictures first to figure out where the bolts are, its a bit tricky but doesn't take too long. One tip is to tie a bit of string on to your wrench as you'll probably drop it a few times. The string will make it a lot easier to retrieve.