How do I tell my mom I need to go to the gyn?

I live a country where parents and children or school do not raelly talk about sex and sex under the age of 20 is considered disgraceful. However, I've noticed unusual discharge and I really want a check in the gyn. However, as I've told my mom, she said that it's alright it's probably a part of puberty and she asked the doctors to be on the safe side, the doctors said that it is fine and it happens to a lot of girls and that I don't need a check because I am only 17 this year and that they can't perform tests on kids. However I had a long term boyfriend (first and only) of 3 years and we have had sexual activity (I know this isn't right but I loved him). I do not want to break this to my mom because this will be a big disgrace and will be very much looked down, i know she'll be upset - I'm the only daughter (i have brothers), i have above average grades and great friends. We do not have planned parenthood here and the public health service is pretty bad unless I go with her.. How can I break it to her or tell her that I really need it?