I am totally in your boat. It's hard to be single and still be happy. The truth is though, you can't be fully happy in a relationship if you're unable to find happiness on your own. To have a successful relationship, you have to have a storage of happiness you want to share with the person you love. If you don't have that already, you have nothing to share with them, and you leave them to try and create happiness for the both of you, and that can be difficult.
To be happy on your own, you have to learn to love yourself. You may have imperfections, flaws, or things you dislike about yourself, but you have to learn to accept and love those things in order for someone else to love them too. So maybe your hair isn't great or you're not the weight you wish to be, learn to love those things about yourself anyways. You are unique and you are special, every little odd thing about you is what makes you fantastic.
Find things that make you happy. Get a hobby that you really enjoy participating in. Create a group of friends (it doesn't necessarily have to be large) that you can relate to and get along with. Surround yourself with positivity and things that will make you smile constantly. Find joy in little things like your favorite scents, that awesome pair of shoes you wear too often, or that hilarious joke only you think is funny. Delight yourself with what makes YOU happy! And don't worry what anyone else thinks.
Get out, exercise and eat healthy. This may seem irrelevant, but trust me, diet and exercise can do wonders. If you spend to much time inside, eating junk food and watching TV/sitting at the computer, you spend more time sulking in the fact you don't have a partner. When the reality is, you have so much potential to be a great person all on your own. Eat a nice juicy apple (it'll make you feel good from the inside out!), get outside, and show the world how awesome you are!
You really are a magnificent person, and you don't need another person to assure you of that. Appreciate who you are and all the great things out there that make you happy. And one day, someone will be attracted to that happiness, someone who will treat you right and love you unconditionally. And all they will do is add even more happiness to what you've already stored up for yourself. Then, you will be unstoppable.
Hope this helped! :)