Tender right side of stomach?!

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seek medical treatment

Your story tells that you are having a hernia, we just need a few more information.
Did it grow bigger when you cough?
Did it grow bigger when you are on prone position? And become smaller when you are in supine?

If it is, it may be a hernia of abdominal wall. Contact your surgeon.
It it's not, it can be anything. Check yourself to the doctor.

Yeah, go to a doctor as soon as possible, today, tomorrow or a next week. You might be having enlarged spleen and it is fatal if it ruptures. Don't lift anything heavy until doctor checks you out. Go to doctor even if the swelling goes down.

That's the general area of your appendix but it could be a lot of things. You are best seeing your doctor. I wouldn't recommend online diagnosis - most websites exaggerate medical issues.