I take omeprazole, but tonight, I'm still having stomach problems. What additionally can I take with it?

Several. You can take an acid buffering agent (tums, mylanta, maalox), an acid reduction agent (zantac, pepcid) or another omeprazole. But try to figure out what triggered the stomach problem (ie something you ate earlier today, extra coffee, etc) so you can avoid the problem altogether. If it happens repeatedly, call your doc.