You may be attracted to girls, or boys, or both. During your teenage years, you are likely to be attracted to all sorts of people in all sorts of different ways – some feelings will be very intense, others milder; some may be more physical, others more emotional; some may last for a long time, others will be over in a matter of days.
This is all a normal part of growing up and working out who you are. Although some people are clear about their feelings early on, it can take time to work out where you are attracted. It is very normal for girls to be strongly attracted to other girls or women as they grow up, but this does not necessarily mean you are gay.
Don’t be too quick to put yourself in a particular category or give yourself the label of straight, gay or bisexual (or any other label). Things are often more fluid and unsettled than might sometimes appear.
The fact that you have sexual or romantic feelings does not necessarily mean that you have to act on them; don’t feel pressured into going out with anyone and always make sure that you are going out with someone for the right reasons.
If you do go out with someone, boy or girl, make it a happy relationship.
The UK is now much more tolerant of different sexual orientations than it used to be and you are protected from discrimination in law. But if you are (or think you might be) gay, you do have extra things to think about – particularly how your family or friends may react.
This page from Childline is a very useful starting point if you have questions about your sexual orientation. It also points you to other sources which can help you with coming out and other issues particularly relevant to non-straight relationships. (It also lists 12 different types of sexual orientation. You may or may not find it helpful to label yourself in this way, but this list may help to show you that there is a wide range of absolutely normal feelings.)