I Am Prescribed Atenolol 100 Mg Once A Day For

I am prescribed atenolol 100 mg once a day for BP. I have been have problems with BP being to high recently and one week ago was in the er because of chest pain and dizziness! All week long when I get out of bed in the morning to get ready for work I feel fine! About 30 minutes after I take my meds my heart starts doing flip flops and I basically feel like crap! Could that be a side effect of my meds or could I be Allergic to Atenelol? And why would my DR or the ER dr not catch this?