Dehydrated

How long would you try and fix the problem with dehydration before going to l&d or Er? I am 30w pregnant, have had a stomach bug for 2 days now and noticed today my urine is very dark and has a smell, I also am not peeing very often, have had an awful head ache. I have called my dr office to talk to them and they said if it gets bad enough to go to l&d. I also have called l&d and they gave me recommendations on what to try. But how long do I try on my own?