whenever i try to wear girl clothes I become erect and one can easily understand that I'm a boy what shall i do??

EDIT: description toned down, =K

I offer a link to our WIKI article on Tucking.  I hope this allows you to venture out into society as female without undue discomfort.

I hope this helps;

Karen

Repeat wearing girl clothes until it no longer responds.

Barbie~

It goes away the more you do it. 

I have been crossdressing Once or twice every month since last 2 year but iit still it becomes big and erect and when i use the tucking process posted earlier i cant urinate plz help sisters.

I don't know release many times until you can't anymore. I don't know 

i cant release..since im only 15

That's very natural then. You are still young. Be careful.

from what should i be careful?