I have the same thing in exactly the same position. Its a lump that my teeth have played with for a couple of years now (certain its more than 2 but I'm uncertain on how long). I actually thought nothing of it and now want to get it checked as in the mornings - especially if I wake up on my back - it can be really inflamed and painful if I chew it as I do throughout the day.
It did start out around the size just smaller than a pea, but its more like double that now. It used to go completely by the end of the day sometimes, but within the past year it does not.
No experience in this myself at all but saliva gland does seem to be a reasonable explanation as sometimes when I'm eating it can inflame as if I had just woke up, this kinda hurts a little bit if you try and continue eating, but give it a moment or two to chill and you can carry on the feast.
If your like me then you'll avoid surgery at all costs, I will still go to my GP see if he thinks that it is a serious case though, if not then ill just continue to live with it until it becomes too much to handle.
Thaks for this forum it has eased my mind, but i will still just get it checked to be on the safe side.
Take it easy.