How to not feel negative all the time?
To start, thank you for sharing about yourself and I am sorry to hear you are struggling. I'm afraid there isn't a super easy and quick answer to this question. It is really important to know more about what you've experienced and how you've wired this way of thinking. I will do my best to give you some things to help you start but the best thing to do would be to work with a counselor on building your insights and coping. This is something most therapists are equipped to help you with.
The first thing you will want to do is work on your mindfulness. This will be a skill you'll have to practice and build on. Being aware of what things trigger your negativity and what your thought process is will help you to implement the next piece. Journaling these things or making quick notes for yourself so when you are out of that mindset you can reflect on it and see what you can pull to help you the next time.
Reframing is the next piece. When you recognize these negative thoughts or triggers coming up in your mind, taking a second to reframe that thought to be more positive. Again, not a simple or easy task--- it takes practice. If you notice negativity creeping up a lot, saying to yourself "stop" or something you come up with that helps you let it go. That being said, it is important for you to process with your counselor those emotions to continue building those skills. Setting them aside at the moment may be helpful, but don't ignore them.
An important aspect I wanted to make sure to address is the piece you said about feeling low. It sounds like the negative thoughts and feeling directly impacting your overall mood. That must be really difficult for you to hold on to your own, especially considering it sounds like you don't feel confident opening up with your family or friends. As difficult as it must be to share those thoughts with others, it is important you can do so with someone who can help you feel supported, validated and can offer you ways to make the changes you want to make.
The fact that you want to work on this speaks volumes. You are making strides in the right direction and I am confident that you can make improvements with support.