I might be wrong, but it sounds to me like your issue is that your confidence isn't so great at the moment more than anything. It's hard to appreciate nice clothes or a haircut when you feel shit, I think we've all been there at some point or other. And then it's doubly hard because whenever anyone does say something nice, you question whether they actually mean it or they're just trying to make you feel better.

If what you look like now isn't your style, definitely consider changing it. Hair always grows back so don't feel scared to try something new; look at different styles or colours and see which you think would suit your face. If you're at a total loss, ask a hairdresser with a good reputation what they think. It's their job to make your hair look good and suit you, so they have a lot of motivation to give you good advice! If you try a new cut and don't like it, no big deal because it'll grow out and you can try again.

With clothes the aim of the game is to figure what works, build up a core wardrobe of things that work and then carry on from there. What are your best features? These are what you want to draw attention to. What type of body do you have? Dress to flatter it. I admit I'm kinda sucky with clothes - family was never big into fashion - but little things can make a huge difference, even to an unobservant person like me.

Ultimately, you gotta dress in a way that pleases you. If someone comes up to you and tells you that they hate your clothes, they're being rude and you shouldn't take their opinions into account. Have you got any family members or friends you can trust to be honest? Ask them if they like what you're wearing and think it's flattering. Failing that, there are subreddits designed for advice which you can submit a picture to (without your face if you want, to preserve privacy) and listen to advice from truly unbiased people.

Whatever you do, don't get sucked into negativity though. There's nothing wrong with critqueing yourself and trying to improve yourself (i.e. I wish I was in shape, so I'll go to the gym to tone up), but don't be too hard on yourself. Remember that you're trying to accentuate your positive features rather than just blasting on the negative ones. Everyone has a mix or virtues and flaws, so stay positive!