Bug or something else?

My 3 year old seems to have come down with a sick bug last Thursday. He woke up pale, warm and lethargic however he wasn’t physically sick until 3pm that day. After that he perked up and was a bit better and was demanding his bedtime milk so my partner gave it to him and about an hour and half later he was sick again. He then slept through the night all fine. Again, in the morning demanded milk and a biscuit which my partner gave to him but he sicked it back up. About an hour after that he drank a load of water and brought all that back up. I assumed he must have caught a bug so kept him rested all day, tried him with little bits of water that he kept down. He was so hungry and upset so gave him some dry toast that afternoon. 2 hours later he was sick again. That was Friday evening. After being fine again all night, on Saturday we took it slow and offered him dry toast which he kept down. He was fine again all night, he had milk Sunday morning and toast for breakfast all fine. Throughout the day, he had more food, he was happy and playing normal we even went for a walk to get some fresh air.Monday came and even though it had been over 48 hours I kept him home just to let him build his strength up and get back into routine, I basically offered him meals and snacks as normal and he was all fine until evening came. He wanted milk about half 6 so we gave it to him and all of a sudden he was sick again, over 36 hours after his last bout of sick. It’s now Tuesday morning and he’s been fine since. My partner and I are both well. Is this just a bug that it lingering or could it be something else? We are really struggling as we are now on day 6, I’m fed up of being coped up indoors and now can’t go to work tomorrow because it won’t have been 48 hours which means I’m missing out on another days pay. He’s also extremely whiny as he doesn’t understand why he can’t have his milk and snacks as normal and is having lots of tantrums so we are exhausted. Just want everything back to normal now.