My daughter had rotavirus at 14 months. It started on a Thursday and she was vomiting every 15 minutes... literally. She couldn't even keep water down. It was very violent, heaving, even bringing up bile. We saw the doc Thursday and then called again on Friday for advice.
We ended up going to the hospital Saturday night and she was put on an IV for dehydration. The vomiting had subsided, but she was so lethargic it scared me. Just because he has tears doesn't mean he can't be dehydrated. My daughter peed when the hospital staff were checking her in the ER and they said she couldn't be dehydrated since she peed.
Well, once we finally saw the doctor, they did blood work and were shocked at how low her levels were and put her on an IV immediately. They even ran the tests again because they couldn't believe that she could still be up and alert and have levels as low as hers. So, I don't think the pee/tears test is very accurate when assessing such a young child.
If he is still vomiting Thursday, I'd take him into the doctor again or even to the ER just so they can run some proper tests. Since Saturday seems like a long time to me, if you're not seeing improvement. For my daughter, we had the vomiting for 3 days and then it went to diarrhea. Once it turned to diarrhea, that was a real turning point and we could see it was improving. I think the vomiting poses more of a danger to dehydration, but I'm not sure. All in all, it was at least a week.
Also, the ER doc told me not to give her just water and not cold drinks. She said water offers nothing - give juice, gatorade, pedialyte (which my daughter HATED) but not plain water. And offer the liquids at room temp, not very cold or with ice. Apparently, the coldness can be a bit of a shock to the stomach, especially for a little one who's belly has been in such spasms for days.
Good luck, don't panic, but do insist on tests if you feel uneasy about him. I was very surprised to learn how dehydrated she was - it was a wake-up call for us. I also thought that as long as there were some tears and urine that it wasn't dangerous and I was wrong. I'm glad we took her to the hospital, especially since it was the weekend and waiting until Monday was not an option for me.