Do not go to the ER for a stuck tampon, unless you want to spend hundreds of dollars on something you CAN get it out yourself. Squat, bear down and reach up, the vagina is not that deep, you WILL be able to get it out.
That tampon needs to come out. You are at risk of toxic shock. If you squat you may be able to pull it out yourself, otherwise you need to go to your doctor or ED and get it pulled out.
you never mention having even taken your tampon out. you had sex. the next morning coulnt find the string, the next day you were having trouble peeing.
you need to be worried about tss not so much a uti, if that tampon is still left in there