What Causes Severe Stomach Pains Extending Up To Lower Back?

hi, im female, 33 and had a bout of gastro about a week ago, there were no cramps just very uncomfortable, the runny tummy has stopped but i have since then had very bad stomach pains and is worse at night , it extends to my lower back (sides), so bad that i am on paint tablets frequently, will this pass or is there something to worried about. i do not have food allergies or intolerances and have never had stomach problems