What Are The Side Effects Of Amoxicillin?

I am currently taking amoxicillin which started 2 days ago- I have high anxiety about taking meds to begin with and am very sensitive. Having taken this antibiotic before, I felt reassured in starting it for a tooth infection. Last night, I developed a hive about 2 hours after taking it and my back and trunk are itchy but no rash. My heart palpitates
for about 1 1/2 hours after taking it as well- no swelling, no trouble breathing- could this be nerves or a true allergic reaction?