Okay, first of all, only an ultrasound can tell you if you are expecting twins. Secondly, it is WAY too early for you to even be showing at all (if your last period was in July, you got pregnant sometime in August, which means you are at the MOST, two months pregnant, which means your uterus is not even expanded enough to come out and over your pubic bone, where it sits), so what do you mean by your stomach is not forming like it should be? If you ARE showing at all, then (even with a multiple pregnancy at this stage)it is most likely bloating and not the actual pregnancy itself. As far as UTI's go, they are VERY common in the general population of women and some women will have more frequent UTI's during pregnancy. Usually, this is no cause for concern, however if the UTI progresses to a kidney infection, or if the number of UTI's is drastically high, things can get dangerous.
You say your uterus is frequently irritated...what do you mean? Cramping? Cramping is common throughout an entire pregnancy and is usually in itself harmless. Cramping can be caused by a variety of things, such as UTI's, the uterus stretching, ligaments stretching, a full bladder, positioning of the fetus (later on), contractions (braxton hicks contractions, often associated with near-term pregnancies, actually occur throughout an entire pregnancy, however, they are usually not strong enough to "feel" early on), or possible miscarriage/ectopic pregnancy. If the cramping or irritation is severe, or if there is bleeding, you should see your OB/GYN ASAP.

Yes cramps and all of the stuff you said. My belly is starting to form but i thought that it was probly nothing just swelling, could that be so? i thought that swelling was just part of it because i have a belly n it looks like a baby belly and i have some god offel cramps i cant help but cry cause it hurts to much is that bad?
but i was thinking that it was normal since this is my first time carring a baby so i thought that swelling and all thats wrong with me was normal. But my tits r extremily sore i was told that that was a big sign of pregnancy? but thank you for talking to me n helping me out u were alot of help, thank you!

have you even taken a pregnancy test?
a pregnancy test and/or a doctor can determine whether you are pregnant or not.
no one online, and no 'gut feeling' or what someone says, can determine if you are pregnant.
take a pregnancy test, and make an appointment to see a doctor.
and in the future, get on birth control use condoms or do not have sex until you know all the facts of what can happen when having unprotected sex and how one gets pregnant and finds out if they are pregnant.

I had aweful cramps and very early showing with my twins.

i had cramping early in pregnancy as well..but i didnt have twins.
she seems to not even have taken a test to determine whether or not she is pregnant, so shes only going by symptoms.
but systoms that some think are pregnancy, can be just mind over matter.
she could be thinking she is pregnant to the point that she is giving herself symptoms, or there could be something else going on.
but she cant just sudge by symptoms.

Well, that is true. A test is important. Plus any pregnancy it's important to see a doctor right away. When you are 15 and still growing yourself, it's even more important to have proper care early on and through out. Have you told your parents?