At about midnight last night DS, 17 months, woke up. I gave him a quick b/feed and he went back down. Then I heard what sounded like him throwing up over the monitor, so I went in and checked on him and he had vomited up everything he'd had for tea and lots of milk too. I cleaned DS up, changed his sheets, etc, gave him another b/feed and put him to bed again. Then I hear him vomit again, so go in and change DS and change his sheets again.
I then decide to have DS sleep in with me and DH. Through the night DS vomited every couple of hours - to the point that he didn't have anything left in his stomach to bring up. He's quite willing to drink water and have b/feeds, but he seems to bring everything up again eventually.

DS seems otherwise fine - no fever, but very tired of course. I'm a bit worried about him getting dehydrated as he doesn't seem able to keep anything down for very long. Is it worth a trip to the doctors, or does it just sound like a tummy bug that will pass?