i took ONE pill, that night i started getting severe stomach pain...

i took ONE pill, that night i started getting severe stomach pains, then the next day my lymph node was extremely swollen an dmy throat hurt i was also getting chills all day! then i started getting a fever and it keeps breaking and coming back im assuming that im a rare case of an extreme allergic reaction but ive also never been allergic to anything before!!! i didnt even think that it could have caused it but then i read the pamphlet and the side effects in clinical studies and there are even worse symptoms that could occur! be careful