Pregnancy! Oh dear 15 years old!!

So I've been with my boyfriend 8 months we have had sex many times and used protection once. However I'm only 15, I've not got a period this month (due on between 26+) I've recently had excruciating stomach cramps and very weak bladder, also been wanting to pee lots!! My breasts are very tender and I've had a few spots recently and I very rarely get spots I've always had very clear skin. Im really worried and don't know what to do or where to go, my boyfriends willing to come with me to the doctors but my parents aren't the most understanding! I've told my older sister who is 23 though. Opinions please? Kept it on anonymous as I'm only 15 and want this to stay private! Thankyou for any help o can get, should I go to the doctors or will they tell my parents? I thought about the clinic but it doesn't look appealing walking out of a clinic at age 15 so I do not want to go there x