It does sound a bit like your gallbladder rumbling, and lasagne would be classic for causing a problem. You say you didn’t eat much fat but you ate a lasagne… was it a low-fat, low-calorie lasagne? Otherwise, a lasagne is a ton of cheese, meat, and often acidic tomato sauce. Many of them have stats with as much fat as eating chips, or something from McDonald’s. Your gallbladder won’t care whether it’s saturated or unsaturated fat. I see someone else has mentioned the 4Fs of gallbladders going bad - “40s, female, fair, and fat.” But you don’t have to have them all, and you personally don’t. It seems with most of my friends, post-30, female, fair, and over size 6, is enough, which I definitely wouldn’t call “fat.” You’re going to probably want to watch things like the lasagne for your stomach for the next few months and your IBS (which could be gallbladder rumbles now, too, especially if you feel nauseous).
With that said, I do agree your symptoms are pretty vague. It could be your gallbladder, or your appendix, or a problem in your intestines. If you start vomiting, if you develop a fever, if you’re crying from pain, seek help. Then they’ll be able to tell you for sure what’s going on, I hope, and especially rule out appendicitis. If no other symptoms develop except this pain, do NOT take ibuprofen - it’s the hardest on your stomach of the NSAIDs; I’m not even allowed to take it. Take some paracetamol, and make sure nothing you eat for the next 24 hours has more than 5 grams of fat in the entire meal (look at the labels). So when you combine crackers and a cup of tea and something, it should still only have 5g of fat. If it’s your gallbladder, this will give it time to recover.