If my allergies are really bad, do i need to worry about overdosing on allergy meds?

No: If taken as prescribed, you should not have issues at all. Most allergy meds are anti-histamines ... An over-dosage is just going to cause disruptions in alertness, dry mouth, etc. But if your allergy meds aren't working... See out an ENT who does allergy or an allergist. You may be a candidate for immunotherapy - you may get to the point you could stop taking meds all together.

See an allergist: If your allergy symptoms are so bad that you are having to take more than recommended doses of antihistamines, you should see an allergist to determine the cause of your symptoms.