Missing period. I consult a doctor?

My period was regular with a slight difference in date since my first period. And now its late by 10 days though its not that much considerable gap, but i had my s*x nearly a month (20-25 days) back And thus so much worried and waiting for my period. My partner says that he did not enter his sperm but why does my period got delay? What to do if my result ends up positive? To get it discharged Can i take any pill to get period ? Can i know it by any particular symptoms other than those which are common for pms? If i am pregnant how can i know it and do those urine tests available at pharmacies are too early to test if iam pregnant? Can i test my pregnancy with it? Is this gap enough for knowing the true result? Should I consult a doctor ? I feel lower back pain mostly on left side little in right side almost 3/4 th time a day. Thanking in advance And i will be waiting for reply as i am really worried about my missing period .