HELP..my sister has been sick for 6 weeks...chills, sharp stomach pains.?

My 17 yr old sister has been sick for over a month and my mom doesn't have the $ to keep taking her all over the place. She has been to Immediate care clinic twice and she has had 2 ultrasounds. The first time the doc checked for appendicitis (said her levels looked ok) and ruled it out, they gave her a preg test (that was negative), they checked for UTI ( not that either) then they said it could be a cyst on her ovary (ultrasound said not that). Then it continued so my mom took her back- he then said gallbladder- well she got another ultrasound- that looks fine too they said. The doc said he didn't think it was an ulcer or diverticulitis. She's even gone to a gynecologist. They said she had a small yeast infection. I don't think this could make her feel the way she's been feeling. I think it's more to it. She hurts in the lower right abdomen, has chills, sometimes fever, feels nauseaus, has thrown up a couple of times- it wakes her during the night. When we went out to eat for my grandma's b-day she cried the whole time because of pain and she can't hardly eat. What do u think could be going on??