Dear,
STDs are acquired as a result of engaging in unprotected sex with anyone who has STDs himself/herself. The chances of acquiring STDs increase if someone indulges in sexual activities with unknown people and does not use any protection.
If you think you have been engaging in such activities, there are chances that you have acquired STDs.
Next Steps
Please don't have any judgment about you have STDs just by reading on internet. Please remember that half baked knowledge is always harmful.
Kindly discuss only with you parents. They may be angry at first and might scold you but since your health is their first priority so they will definitely understand and take you to a doctor. Try and speak to any family member with whom you are close enough and can share your secrets. Then that person can facilitate it ahead.
Take your parents to a dermatologist who is an expert in sexually transmitted infections.