Medication Stopped & Palpitations

I just want to rant and see if anyone can relate to my issue. So I used to be on Methylphenidate 36mg but due to it increasing my heart rate, I decided to stop the medication. It's been 2 weeks today since that happened, and weirdly enough, I experienced the same palpitations I had on that day 2 weeks ago. I only get palpitations after I eat for some reason and at the same time, my stomach hurts. Mind you, I haven't been taking the ADHD medication for too long (18mg 15 days and 36mg 8 days) so I'm not sure if these are withdrawal side effects or if something is actually wrong with my body. I have contacted my GP about it and they scheduled me for 26th March (which is quite far away). I've taken a blood test and an ECG, everything was fine. Has anyone experienced this? If so, was it because of the medication or was it a different issue?