Pain in mid upper stomach?

Since Wednesday night of last week, i have been experiencing severe pain in the upper middle part of my stomach. i feel like everything is "coming up" and kind of like choking from that and i need to vomit in order to feel better. I sometimes get real hot and my face feels flushed and then i sweat. I've felt nauseated and bloated and kind of feel like i may have to use the bathroom or something. I'm also burping more frequently. it somewhat helps when i lean over but the relief is barely noticeable. this pain also wakes me up during the night. I've been to the dr and they put me on omnoprazole?sp? lactulose & phenegren?sp?. i've had xrays & an us of my gallbladder-i never really got the report just a "nothing really pertinent" on the us. could it be gall stones and just may have not shown up? and if so, do the attacks occur frequently ie. about 15-30 mins after every meal and last from 1-several hours. i've had about 10-12 since last wednesday