Sounds like possible side effects of your medication:
mercaptopurine Oral Side Effects
Nausea, vomiting, diarrhea, and loss of appetite may occur. Temporary hair loss may also occur. Normal hair growth should return after treatment has ended. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
Tell your doctor immediately if any of these unlikely but serious side effects occur: easy bruising/bleeding, dizziness/fainting,
joint pain/swelling, tongue/mouth sores or pain,
unusual tiredness, symptoms of liver disease (such as persistent nausea/vomiting, stomach/abdominal pain, dark urine, yellowing eyes/skin).
Tell your doctor immediately if any of these rare but very serious side effects occur: symptoms of possible lymphoma (such as swollen or painful abdomen,
persistent fever, night sweats, unexplained weight loss), change in amount of urine, pain in the lower back/side.
This medication can lower the body's ability to fight an infection. Tell your doctor promptly if you develop any signs of an infection such as fever, chills, or persistent sore throat.
A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any of the following symptoms of a serious allergic reaction: rash, itching/swelling (especially of the face/tongue/throat), dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.