My dogs throwing up, any ideas to what i can do, or what it is before going to a vet?

i bought a female boxer that just had a litter 8-9 weeks ago and i had mentioned to the person that she looked skinny but they said it is what happens after having pups but since i have brought her home she hasnt really eat much and or drank much either, i know it could b from the move and i dont have any idea what they were feeding them because they didnt have any food or left over food to send with us, but she keeps getting sick, its not food coming up its yellow like, what could b wrong? i cant afford to take her to the vet right now, but what can i do?