Is this signs of early pregnancy???Help !?

okay so my period was supposed to come on the 15th and its now the 18th and it hasnt come, and ive had cramps like period cramps since about the 11th and still have them and ive had headaches and im wondering could this be a sign of pregnancy me and my boyfriend have unprotected alot and he usually doesnt *** in me but he did a few times about 3 or 4 weeks ago im not on the pill or anything neither..could be pregnant