You can in most cases go to the doctor without your parents knowing as long as you're at leas 13 years of age or older depending on the state you live in.
In most states, minors are allowed to receive confidential care for some health issues, which include STD testing, which parental consent or notification to the parents that you received the care.
Although some factors like a specific state law, the type of treatment you're looking for and the doctor's policy can also factor into whether or not you can see the doctor and seek treatment without your parents knowing.
Some states have their own different rules so it will depend on your state and their laws.
And many doctors will also agree to keep your medical information confidential as long as you're 13 years old or older, which means that the doctor will not share the medical information with your parents or anyone else unless you give them permission to do so.
As long as you're 13 or older you can often get confidential care without your parents consent for STD testing, pregnancy testing, contraception and mental health services without your parents knowing about it.
However it's a good idea to talk to your doctor about their privacy policies and what you can expect from them and you can also ask them about accessing confidential care at a health like such as planned parenthood.
Although if you're are looking for or need a major medical procedure done, or if the doctor does believe that it's necessary for your own safety, then they may want to involve your parents in the decision making process.