I get whiteish discharge a lot and I just want to know what it is, is it anything to do with being sexually excited. I'm just worried that when I come to have sex it will all be there and its not very pleasant

If there is no odor, discharge is normal and healthy in a woman. You should only be concerned when there isn't any, or if there is a foul odor.

Your white discharge is more than likely cervical mucus and it is absolutely normal for a woman.
Cervical mucus often appears prior to ovulation (when your ovaries let go of those baby-making eggs). Sperm requires cervical mucus to survive. In the presence of cervical mucus sperm may live from 3-5 days and wait for ovulation to occur. One way to think of your cervical mucus is as nature's gate. The gate is open when the mucus is flowing and sperm can enter your uterine cavity. It nourishes the sperm and allows only viable sperm to make the journey to your egg. The discharge changes in consistency as you approach ovulation. Many women continue to notice smaller amounts of discharge right up till you get you menstruate.
For some odd reason, many women experience greater sexual arousal when your cervical mucus is present. Sex and all your bodily functions might seem a bit embarrassing but it will be a beautiful act when you reach a mature age and share it with someone you love whom loves you.

The above answer is good, however, cervical mucous also prevents pregnancy. Thick white cervical mucous does not allow the sperm to get to it's desired location as it is too thick for the sperm to move through and it also is slightly more acidic and it breaks down the sperm.

When your cervical mucous changes to a thinner, more watery, yet sticky discharge, this is when the time is optimal for pregnancy to occur as explained perfectly above.

Your vagina is a mucus membrane not unlike your mouth. Your mouth makes saliva and your vagina mucus. Many, many things can impact the quality and amount of vaginal discharge. For instance hormone levels, medications, infection and sexual activity. For women not on hormones typically the discharge just after your cycle is thick, sticky and dries yellow to white on your underpants. As you move closer to midcycle and your body prepares for ovulation the discharge becomes runny, slimy and a bit clearer. If you don't conceive it gets more tacky and sticky and then your period will begin. At no time should it burn, smell or itch. Prepuberty and post menopausal females will have a much different quality and character of their discharge. So what you are experiencing is normal and healthy.