My 3yr has pains in her arms, legs and complained of tummy ache for 2 mnths, doc said nothing, now headaches, tired and has had 1 weird hallucination?

Go back. The list of possible causes to her symptoms is long. She may even have a central nervous system issue or infection like lyme disease. Often with a variety of symptoms as hers, you aren't given a diagnosis the first time you're evaluated so she needs to go back and ask the doctor to re-evaluate her for other causes. If you aren't comfortable with the evaluation and diagnosis get another opinion.
Plumbism? Child with abdominal pain associated with leg pains etc make sure lead level is normal check also for sickle cell anemia go back to your doctor for evaluation.