Advice on medication

Hello

My son started on Methylphenidate for adhd (he has severe learning disability and autism) he began on 2.5mg twice a day on school days, he seemed to have some loss of appetite at school but we didn't notice this at home and he appeared  to be eating  well. After 3 weeks he kept saying 'ouchy Tummy' and we did see a decrease in his appetite this continued for a few days and he was eventually sick (we assumed a bug) and he was fine after. Medication  appeared to be  having  a positive effect at school so our dr upped the medication to 5mg twice a day. He had a week off all medication for the half term and restarted this new higher dose last week (weekends off) on Sunday he was saying again 'ouchy Tummy' and has gone off his food. He has then had sickness tonight.  

We are very new to medications  and knew of the serious side effects to look out for but I don't remember  seeing sickness being one of them I was wondering if anyone thinks there could be  connection or son/daughter had similar  problems. We could just be very unlucky and have 2 bugs in a matter of weeks but this isn't usual. 

Thanks for reading 

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