15 Week Old Kitten, Vomiting As Soon As She Eats, Constipated.What's The Matter?

My 15 week old kitten has not been able to keep her food down for the past two days. We took her to the vet this morning, who said it might be a hairball or something else got lodged in her gut. We couldn't afford the charges for X-Ray and surgery, so the vet gave us liquid parafin to lubricate her tubes. Is there any other advice that will help me for now? Also, what other, more serious symptoms should I look for? Thank you.