I Think My Puppy Might Be Sick?

I have a 3 month old maltese/shih tzu please no insults about him being a mutt. This morning my mom took him for a walk in a newer area, it was a big grassy hill. She came home and said he ate A LOT of weeds and a rose petal. Half an hour after, he started throwing up, he threw lots of weeds and some of his food, we thought it was no big deal. Then he fell asleep, then woke up again and threw up some more but very little. He continued to do this throwing up very little at a time, until he just started throwing up some whit liquid, So the last time he threw up was about an hour and a half ago. And he's just sleeping or laying down he seems to have no energy and he doesn't want to drink, my mom says not to worry yet. The vets not open today but she has an emergency number and does housecalls? Should I be really worried, I dont want anything bad to happen he's my baby and I hate seeing him like this. Advice please, has this ever happened to you? :'(