If you are 4 months pregnant and yesterday you started throwing up every 30 minutes and cannot stop What should you do?
Poor you! Let your doctor know. It could be that something you ate disagreed with you, or some passing stomach bug, as it sounds so violent and came on so suddenly.
Try to keep sipping water, so that you don't get dehydrated. I know its difficult to keep on drinking liquids if they just keep coming back up again, but do keep sipping water or any other soft drink that you can face.
Sometimes, women get sickness in the second trimister when they didn't have it or have it badly in the first, but this sounds as if its a passing thing because it's so violent.
Above all, let your doctor know, just in case it goes on for more than a couple of days. If so, he will probably be able to give you some anti nausea drug that has been proved to be safe for the baby.
Hugs and sympathy