Depends on what the antibiotic was prescribed for. The symptoms could have very well been related to the illness. Also some things are considered "side effects" and are expected; such as some drugs that cause dry mouth, others that can cause nausea if not taken with food, etc. To have these symptoms would be to experience a "possible side effect", and not necessarily an allergic reaction.

I am personally allergic to some dyes and preservatives, which cause rash and hives. This was confirmed an allergy after symptoms led me to have a patch test at an allergy doctor's office. I am also allergic to penecillin but it causes breathing distress.

Sensitivity is an intense effect of medication. I get very wired on diphenhydramine (bendryl); docs call it a sensitivity. My Aleksander dog gets high liver enzymes for months following prednisone and he needs a LOT less than the standard dosage- also a sensitivity.
Usually an allergic reaction to drugs involves anaphylaxis- tightness in throat and chest, trouble breathing, possible swelling- and can be life-threatening. Allergic reactions are actually hypersensitivity that send the body into an over-reactive response.
Intolerance is just a fancy way of saying that the treatment is worse than the disease; usually a side-effect of the drug. That could be anything from dizziness to chronic explosive diarrhea to seizures or anything else that makes life unbearable.

:) an allergy is a histamine response- the body's immune system freaking out over something introduced into the system. the most common byproduct is swelling, which can be life-threatening when we're talking about swelling of the throat, or airpassages. the treatments usually involve adrenaline in some form.

a sensitivity is just that- where you have a much stronger response to a drug than the dosage would indicate. I'm sensitive to most pain killers and ephedrine- half a sudafed hits me like it's a street drug (and splitting a sudafed is a pain)

intolerance is just that-and Keflex is famous for making people nauseous- I'm pissed at your doctor for not mentioning it to you ahead of time! it has consistently left me feeling WORSE than whatever it was that earned me the scrip.

For example: Everyone is sensitive to black pepper. It makes everyone sneeze. That's sensitivity. If someone starts sneezing even if the odor is faint, that's intollerence. It's sort of a problem with degree. Now, if the pepper gives a person hives, or they get asthma or sneeze so much that they can't draw a normal breathe, that's an allergy.. That's a very simplfied example but it's the same sort of thing with drugs.