There's no such thing as "normal". But your 'fainting' isn't normal, -(the posh name for it is SYNCOPE
incidentally pronounced "SYNCOPY"). It may be hereditory, or a slight malfunction of the pulse-rate response mechanism which should kick in when you stand. It is typically associated with females of your age and will greatly improve as you mature.
You can test it simply by rising carefully from a sitting position, and measuring your pulse before and after. Be careful, of course ...and simply try to test your pulse-rate's speed of response. This is a standard test and pilots have to take it regularly when their flying-licence medical is done.
It would be good to chat about it to your doctor, but not a huge amount is known about syncope, so don't expect too much from him apart from sympathy!
Practically, it IS possible you may alleviate the problem by clasping your arms across your chest and "hugging yourself" tightly with hands behind your back, just as you gently stand up. The theory of this manoeuvre is exactly the same as is used in high-speed flight. Pilots use pressure-suits which prevent blood from flowing down (out of the head and upper blood-vessels) from the brain to the trunk and lower limbs
. If they didn't have the pressure suits on they "Black-out" during high-G turns.
Doing the "hugging yourself" thing is a primitive but often effective way of helping to relieve syncope.