What Causes Severe Cramps And Bloating While On Naproxen?

I was taking naproxen for back pain and last wednesday I started getting horrible cramps and bloating. So i stopped taking naproxen on saturday morning. Saturday night my throat started to feel like it was swelling up. It has been a couple of days since I have taken naproxen and my stomach is still bloated and feels worse at night and my neck is still swollen.