What could be causing my sudden nausea and loss of appetite?

I'm 48, female, and absolutely NOT pregnant. I had a physical just last week; unfortunately, this symptom didn't start until the day after. I only think about food when I realize it's meal time and I need to make something for my family. But I usually don't eat, or eat just a tiny bit. My appetite is nil. I just force myself to eat a little something now and then because I feel I should. Every few hours, I'll suddenly begin to feel mildly nauseated. The first few days, it would just last a short time, but today it's been several hours straight. I've wracked my brain to think of what might be causing this. I do take a lot of medications, but I've been on them for years. The only thing new in my regimen is an Omega-3 fish oil supplement I started taking. It's 2000 mg a day. Could this alone be the cause of my stomach troubles?