I experienced many side effects from Lithium, but not quite the ones you mentioned. I did have a change in my skin and finger nails, though. I also used to read that some get a slight metalic taste in their mouths.

I was always on way more than 300 mg, even from the very start. The first time I was put on it I was put straight on 1,200 mg. The second straight on 900 mg. I almost always had polyuria/polysipsia (extreme thirst and very frequent urination. Because of this, I drank a very large amount of water. Drinking a good amount is recommended, anyway. Dehydration can lead to Lithium toxicity, especially on higher doses, unlike yours. Perhaps more water may help your throat? And/or a lozenge of some sort?