What could be going on with me?

I've been having a lot of headaches, im tired all the time, my weight has been drastically changing up and down within short periods of time, I get dizzy for no reason and I sweat all the time weather its hot or freezing. I've also been having stomach problems. I have to use the bathroom before i even get finished eating and more times than not i have very loose stools. My moods have been changing and i easily get angry. Im 28, not pregnant but breastfeeding. Can anyone tell me what might be going on with me? Thanks to all that answer.