It depends on your cycle as to whether or not you are likely to get pregnant on your period. If you ovulate right after your period (which some people do!) you can get pregnant.
Also, you can get pregnant from precum and I doubt it dried in five minutes.
You most likely are not pregnant, and I would try really hard not to worry, but these things do happen to people!
Symptoms of a bladder infection are burning when you go, having to go frequently, sometimes your pee will smell strong.
You can get bladder infections (and yeast, bacterial vaginosis) from sex(that being the main thing!), wiping from back to front instead of front to back (gross, I know and I can't imagine anyone doing that, but people do!), wearing underwear with a colored crotch, baths, bubble baths, etc.
There are lots of other causes but I can't think of any.
You can help prevent them by peeing right after sex (wear condoms every time it also helps), take showers and not baths, wear underwear with a white cotton crotch (this is mainly for yeast infections and bv) and drink cranberry juice.