I feel fine all day. Then, after dinner, I feel ill. I get really sweaty and feel like I have heartburn. Later on, my stomach hurts.?

? Gastroparesis. What you may be describing is stomach dysmotility. A stomach that is slow to empty will feel progressively fuller as the day progresses, resulting in gastroesophageal reflux, abdominal distension, & resulting autonomic symptoms like sweats, nausea, lightheadedness. Have you been tested for diabetes? Have you had stomach ulcers that may have narrowed the stomach outlet? Get it checked out please.
Maybe you do... Have heartburn, that is. We also sometimes call it reflux or gerd (gastroesophageal reflux disease). This can cause some of the symptoms you describe. I'd start by limiting my intake of alcohol at dinner and avoiding anti-inflammatory drugs like naproxyn and ibuprofen. Trying an over the counter agent like Prilosec or Prevacid (lansoprazole) can help greatly. Talk to your doctor if you don't improve.