im 16 years old and im 5'5 and weigh 9/10stone , im not sure when my last period was but it was around novemeber , i had sex with my boyfriend in that month and we used condoms but im now concerned since ive missed my period , ive felt really sick for a few days now even though ive not physically been sick , ive also had stomach cramps & head aches , could i be pregnant ?