How are you feeling Tara? Did you see someone? It's good that you don't normally get gastro but do try to remember that when we're pregnant, our immune systems are low which makes us more susceptible to illnesses - even if they're not ones we normally get. I had three cold sores in three weeks early in my second trimester!!!
Symptoms of dehydration vary but some common ones include disorientation, lethargy, dry cool clammy skin, excessive thirst, headaches, blurred vision. Don't over do it with the gatorade - make sure you keep up the water. If you have too much of a drink like gatorade it can cause lose bowel movements. If you're worried about dehydration to the extent that you are wanting gatorade, you would probably be better drinking something like gastrolite but check with the pharmacist to make sure it is ok for pregnancy. If you're concerned about electorlyte balances, I recall reading a little salt in water is fine as an alternative to plain water but should not be done regularly without doctors consultation.

HTH and hope you feel better soon.

MG