3- Allergies

From Merriam-Webster Medline Plus Medical Dictionary - the definition of "allergy"

1: altered bodily reactivity (as hypersensitivity) to an antigen in response to a first exposure <his bee-venom allergy may render a second sting fatal>

2: exaggerated or pathological reaction (as by sneezing, respiratory embarrassment, itching, or skin rashes) to substances, situations, or physical states that are without comparable effect on the average individual 
In a serious healthcare situation, we pretty much only care about the first kind of allergy.  Medications that cause these reactions should and will be avoided (with a few exceptions which I won't get in to here).  If you have allergies of the second kind, we'll try to avoid those if we can but if those medications are the best choice then we may use them anyway and just keep an eye on you.

There are two points I hope you you take from this:

1- When your doctor asks you if you have any allergies to medications, s/he asks because s/he wants to avoid killing you, not because s/he wants to avoid giving you an upset stomach.  Therefore, please do not tell your doctor that you are allergic to codeine because "it makes you want to puke".  On the flip side, please DO tell your doctor that you are allergic to penicillin if it makes your throat swell closed.  Note that no where in the above definitions is "upset stomach" considered an example of an allergic reaction. 

2-  When your doctor asks if you have allergies, please tell the doctor WHAT the reaction is so that your doctor can decide whether or not your reaction is a true allergy and whether or not a situation might warrant using the medication anyway.  Do you want your doctor to hesitate giving you pain medication because s/he isn't sure if your "allergy" is a true problem?  Do you want your doctor to hesitate to give you the best antibiotic for a life-threatening infefction because s/he isn't sure?  If you don't tell us which of the two kinds of allergies you have to a medication (or if you call something an allergy that really is not), then we kind of have to assume it's the worst kind and avoid the medication.

At your service,
The Happy Pharmacist :)