Gabby, You could have a hernia. The stomach wall (abdominal wall) can open. Best suggestion is to see a doctor. With weight gain being an issue, you may want to learn about diabetes and how to cut back on sugars.
You said this started only a few days ago. It could still be a reaction to something you ate recently. Maybe you bumped into something and don't remember. Careful with aspirin....ibuprofen...
It sounds like a stomach ulcer. Check with your MD, he may want you to get some tests done. Stomach ulcers can be very painful.
Go to the doctor. Any tearing to burning sensation in your chest is bad.
I lost 65 in about one year. I had the exact feeling above my left thigh, kinda in my pelvic area. So my doctor did a sonogram looking for a hernia or something on my overies, Nothing. Now it's just numb there. Just last week I felt like a rubber band keeps snapping under my left arm pit from my rib cage to my chest. I am a bit scared. If you get any answers, please let me know. I hope you are doing well as your post was 2 months ago.