What Causes Swelling Of Face And Hives On Body?

I have been having episodes for the last 2 years of random swelling of certain parts of my face with no found allergen. I have seen doctors about it and they conclude the "angioedema" may be stress related. It can happen if I get bumped then that area swells tremendously. sometimes I wake up with my lip all swelled up 2-3 times its normal size. I now have over past few months began getting random hives on various places on my body and they are red and very hot to touch. I am now taking claritin every day and have recently started adding zantac daily per my doc reccomendation but would like to know what is wrong with me.