Unexplained illness

A couple of days ago, William woke up from his afternoon rest. I was feeding Samuel in my room (I have a breastfeeding chair in there, and Samuel sleeps in there too - my room that is!), William came in and was looking a bit pale, but I thought it might have been from just waking up. He was lounging around me on the chair. All of a sudden he stood up and vomited all over my legs. While I was feeding. It was everywhere. He ended up in the shower, was happy enough afterwards but didnt want much dinner - understandable.

Last night while he was telling me he was hungry. "When's my dinner coming?" We had pork chops, salad and chips. It was a little bit past dinner time, all dinner times have been a little later than out usual 6pm since Samuel was born! Once his dinner was in front of him he didn't want it. We put it down to typical toddler behaviour. There was some trying to force him to eat, trying to reason with him, some questions "I thought you liked chips?" William-"I've had enough".
Then, all of a sudden - yep - another huge vomit. Everywhere. Into the bath this time. After the bath, he was hungry again and ate some pasta - no sauce. He went to bed and was fine.

This morning, woke up, came into our room, declared his hunger and ate some toast.
We decided to go out for breakky, he seemed fine and said he wanted pancakes.
Everything was going fine, William had his pancakes, so did Ben. I had french toast.
Not even halfway through his pancakes another completely unexpected projectile vomit. Over the table, over the chair, over the breakky and over the floor.
"Why did I spew?" were the first words out of Williams mouth. The next were "why is she taking my pancakes away?" He was completely fine before and after and even managed to eat another pancake.

Now? He looks a little pale, we convinced him to have some Gastrolite. He's eaten an apple, played like normal, been running around like normal.
What should I feed him tonight? I want to get him looked at by the Dr tomorrow but I am sure they will tell me it is a virus. It is always a virus. But is it a virus if he is completely fine before and after? With no temp and no diarrhoea?

This is what he is doing now...