I need more information regarding the medication that you take daily.
Welcome and thank you for posting your question.
You said that you are diabetic and have also Parkinson
I need to know what medication you take daily.
Many patient with Parkinson develop itching because of the excipient of the tablets of Levodopa (Sinemet). If you are taking this medication already then you need to rechange it to a different Levodopa.
You can talk about this with your doctor and get another Levodopa with prescription.
Meanwhile apply on the itching area cream with antihistamines locally. You can get this at your local drugstore without prescription.
Hopefully I helped to direct you to the solution.
If You have other questions, feel free to post them.