I'm 17 and took 3 loratadine tablets, 10 mg/ antihistamine in the last 24 hours, are there going to be any issues i should be worried about ?

Probably not but...: Long acting anti-histamines should not be used more than one in 24 hours. Taking more has been associated with heart issues but that is still unlikely to occur. If you have any chest palpitations you should be evaluated. For future reference, these medications can take 4 - 6 hours to work. If you are still not getting relief you can safely add a short acting anti-histamine (Benadryl).