I just want to go through phases like puberty and I can't stop thinking about sex. What should I do?

If You're 28yrs old, --then you have already gone thru puberty! If I understand the question correctly though,you're saying that you currently have high sexual desire (sex drive) which causes you to think about sex a lot.All normal at age 28!Without knowing your views on sex, though, I can't advise you about how to handle this. It would be appropriate to see a therapist to discuss the stage of development you are in.
Relax, stay focussed. You should talk with someone with whom you can discuss such intimate feelings. You should be sure about long term commitment and safety before becoming intimate with someone. You can experiment with acts like masturbation that can provide sexual pleasure, until you finalize on your sexual partner. Be safe!