unknown cause for random swellings all over body

I have been having random swellings all over my body; my thighs, feet, fingers, upper arm, on the backs of my knees. Yesterday I woke up in the middle of the night with one side of my face/mouth/lip swollen. Also one side of my tongue has swelled up, as did my uvula which was quite scary really. The surface skin swellings (arm, thigh) are kind of reddy-purple in colour, otherwise the skin just feels quite warm and fluid filled. They started about a month and and were quite frequent, ie. a new swelling every 3 days, but recently it has been more like one every 1-2 weeks. They don't last more than a day. I went to my doctor who said it was most likely hives, but when one side of my face swells up, or my fingers etc, there's no redness whatsoever and none of them have been itchy. Its just like an inflammation of some sort. I had a blood test and came up negative for any of the allergies. I was just wondering if anyone else has had a similar problem/knows what might be the cause of it.  Thanks