Suck on a peppermint....all day....always have them with you. Peppermint is soothing to the stomach. The hard candies have enough sugar to at least keep you from getting dizzy from low blood sugar and you don't have to swallow anything solid.
Also, I know you said you've tried antacids, but did you try the cool peppermint tums? They are fantastic. They helped me a TON when I had prego sickness. The fruit flavors etc.. never helped but the peppermint ones did.
You can also drink peppermint tea to get the peppermint into your stomach. Try doing this before you eat.
Make sure than when you eat it is in VERY small portions. Basically you should be "grazing" all day and on very bland and stomach friendly foods. I found that mashed potatos worked out well for me when preg. Always carry a bottle of cold water with you too and take small sips when you feel the sickness coming on. This can force it back down and soothe your stomach too. If you can use the water to suppress the nausea long enough for it to go away you should be able to keep more foods down.
You could also try the accupressure wrist bands for motion sickness. I found that these helped a bit with my sickness.
Don't forget to brush your teeth as much as you can stand it. All of that acid can eat the enamel right off of them.
Best of luck to you! I hope you find something that works.