What Causes Excessive White Discharge?

Hi I get extremely wet during inter coarse, Sometimes its stringy and other times its white and thick. It's embarrassing because sometimes its left on my partners bits when were finished. Also I'll be doing every day activities and feel discharge coming out of my vagina. Its always in my underwear but its white and sometimes bubbly. Its been like this for a very long time as i am too scared to go to a doctor. Do you know what's wrong with me and Would this effect my reproductive system if i have left it too long? Thanks