Side effects of Azathioprine?

Today has been one of the worst days in a long time! It started off fine, I took my medication with breakfast like normal and decided to go to the car boot sale with some of the girls despite having a bit of a stomach ache. Walking round I started to feel a bit sick and the pain in my stomach was getting worse.  As we headed back to the car we stopped to get a bottle of water but I couldn't even stand in the shop I had to walk round the corner down an alleyway where there was a bin and throw up. Not one of my best moments (didn't even have the excuse of being hungover!) but at least it was outside M&S so I could maintain some class! I managed to get home thanks to my friend driving me back and have spent the rest of the day in bed being sick and having a massive tummy ache. There is no point in paracetamol or other pain relief as I would just sick it up so all I can do is ride it out with my hot water bottle!
The hospital recommended I go straight to A&E and be transferred to the gastro ward where they had a bed waiting for me but the thought of spending New Years in hospital is horrible. If this feeling is because of the medication then I know I should go, but if it is just a bug then going to the hospital will make it worse for me and everyone else on the ward. Has anyone else had side effects like this on Azathioprine? Very confusing!