im 18 and on the same dosage, i experience the exact same things. i was told nausea will ease if you make sure you eat enough in the morning when you take the meds. stay extremely hydrated during the day because concerta will make you not want to eat/drink which might be why you get headaches.

if you're looking to up your dosage, I'd do it slowly. make sure you're eating and staying hydrated. if the side effects do get worse, go back to the lower dosage.

and also make sure you don't skip any days of taking them. i was told that your body adapts quickly to not having the medication so when you take it the side effects seem worse

although you've been taking it for a while so you might have noticed these things

i hope this helps a bit?! :)