Could it be an ulcer, gas? Something else?

Okay. So I have been having noticeable stomach problems for about two months now, probably slightly longer. It started with just stomach aches that felt abnormal, then over the past couple weeks I have been experiencing sharp, sudden pains in my upper stomach/chest area. It moves a tiny bit, but usually stays around my right rib/breast and sternum. These attacks usually last anywhere from twenty minutes to multiple hours. Quickly after it begins nausea sets in. I went to my doctor about two months ago when I first noticed the weird aches. He perscribed a medicine for gas i believe, a small pink pill. I do not take any other medicine besides that, naproxen sodium (for cluster migranes, i've been taking it for about four years now as necessary) and ibuprofen (for cramps). My mum thinks it could be gas, but i think it could be an ulcer. Could it be something bigger? If you need more info feel free to email me at connies_for_chuck@yahoo.com.au