I have been taking cymbalta (duloxetine) & concerta for 4 days in the morning. i took motrin and claritin for my allergies and feel slightly dizzy/weak?

Not likely meds...: Allergies often affect fluids in the middle ear & may explain "dizziness". I would not expect the combo of meds you mentioned, to be "causing" the problem: Concerta is a stimulant; cymbalta, (duloxetine) an anti-depressant. Drink plenty of fluids to mitigate against dehydration playing any role in your feeling weak and/or dizzy.