You have a definite allergy to Penicillin.
You also have an allergy to the cephalosporins--
Penicillins--Penicillin, oxacillin, nafcillin, etc. (basically look out for anything that ends in ...cillin). Also watch out for Augmentin (amoxicillin and clavulanic acid).
Cephalosporins--they have a similar structure to the Penicillins. Cephalexin, cefaclor, etc. generally begin with cef.. or ceph.. . About 12% of the people who have reactions to pen. also cross react with the cephalosporins.
The mechanism of action of both are similar--they interfere with bacterial cell wall synthesis.
Tetracycline, Erythromycin, and Minocycline are inhibitors of bacterial protein synthesis. Tet. and Min. are in the same family (min. is a semi-synthetic tet.) . Erythromycin, clarithromycin, azithromycin are in a different family.
Sulfonamides (Sulfamethoxazole/trimeth.) have an antimetabolite effect on the bacteria.
Different classes of antibiotics are selected based on the suspected bacteria, where it is on the body, clinical signs and symptoms (and what the Dr. has found useful in the past).
Cipro is a floroquinolone (inhibits nucleic acid metabolism in the bacteria), and is in the same family as ofloxacin, etc. (ending in ...oxacin).
Doxycycline is in the Tet. family, and may cause the same problems. One of the side effects for Tet. is "macropapular erythematous rashes" which might explain the scabby spots you had.
Definitely tell anyone prescribing to you that you have had the red spots when you take Pen. or the Cephalosporins.
My board review packet for Pharm says that 1st choice for Bacillus Anthracis is Penicillin G (which you are allergic to) and second choices include Erythromycin and Tetracycline.
However, any Biowar bacteria is going to be resistant to many antibiotics, so that would definitely change things.