Hello Aron,O.k. Urinary tract infections are always a pain in the...well...you know. Pardon my bluntness, but are you sexually active? I can't make out from your name whether you are a guy or a girl, but here's the scoop on the swab. Although your stomach pains may be caused by the antibiotics, if they are severe and the doctor is thinking swab, he/she may be thinking gonorrhea. Gonorrhea is often associated with severe stomach pains. Sometimes it can be detected via a urine test which tests for nucleic acids, but understand that urine is not necessarily a great environment for the survival of nucleic acids, even under amplification. The swab is a much more effective in detecting it these nucleic acids. Thankfully, gonorrhea is an easily treated bacteria. The medicine you are on is actually a treatment for it. I'm not saying it is gonorrhea, I'm just telling you what the entire swabbing may be about.Can bacteria survive in your system without symptoms? Sure. You have thousands/millions of different strains of bacteria in your system...most of them harmless. Even the harmful ones can stay in your system, asymptomatic, until the body undergoes a homeostatic shift and then they attack. Hey, it happens to everybody. As for the entire strep thing, it would actually be more the case that if you had been on zithromax before, that there would be resistance to the drug, making it less effective, than if you fought off the strep yourself. It's called an antibiotic resistant infection/strain. Without initial exposure to zithromax, drug resistance isn't likely to appear in the infecting bacteria.Sternum pain isn't that uncommon, especially when you're having a D/stomach pain day. The diaphragm is closely associated with the digestive tract. It may also be caused by hyperventilation, which, given the shakiness that you're describing, may well be a possibility. If the chest continues to hurt, you may very well have pulled (or inflamed) a muscle. I suffered for a long time with what felt like a heart attack every single day until I was diagnosed with having costochondritis which is a similar inflamation. A shot of cortisone at the top of the rib cage cleared it right up...almost within a couple of hours. So, there's really nothing to worry about here at all.Important thing to remember is to just stay calm. Everything will be o.k. If not now, then in a couple of days. Be sure to drink plenty of water to keep your blood pressure stabilized, especially when on antibiotics and having a urinary tract infection. You'd be surprised at how much better just a glass of water may make you feel. Just take it easy and everything will be fine.Doc