Hi Jacqhar,
One or two in the States have mentioned the metallic taste but it tends to wear off in a few days. The nausea is your body's reaction to what is in effect a foreign substance. Generally if you are going to experience it, this will start within the first 2 days. If you do find you are feeling queasy, just try doing the injection immediately before you eat - many people find it helps reduce the nauseous feeling. The nausea (if you are going to get it - 44% do, 56% don't) generally wears off in a week to 10 days once your body becomes acclimatised to the byetta. Unfortunately it comes back again when (or if) you move up to the 10mg pen, but again it only lasts for a week or so.
I presume you are still on the metformin and Amaryl? If so then you will need to watch your BG very carefully because the Amaryl, when used in conjunction with byetta, can cause a hypo. If you find your levels are dropping too low, just ask your GP if the Amaryl dose can be reduced. The Amaryl you are taking simply forces the pancreas to produce insulin. Byetta mimics the incretins that tell the pancreas to produce insulin, so by taking both meds, your pancreas can end up producing too much, hence the hypo. The fact that you dropped lower than you are used to before lunch is evidence of the additional insulin your pancreas is producing, which is why you need to monitor the situation.
Well done - sounds like you have made a good start.