If you're allergic to penicillin, you'll most likely get doxycycline 100mg tabs twice per day for 10-14 days. The other alternative is clindamycin injections for 10-14 days... which they probably don't want to do.
Definitely get checked. Go to Planned Parenthood or your PCM or something.
Edit: also worth looking into WHEN you got diagnosed with an allergy to penicillin. Many children have to take it at some point and break out in hives but it's a transient allergy during childhood.
An allergy panel can sort it all out.