This is a very serious issue, because not only is having sex with animals physically and emotionally dangerous for both the person and the animal, it is illegal in most states, carrying either a large fine, jail time, or both.
During adolescents and early adulthood it is very common for both males and females to explore their bodies and experiment with sex. As you become more aware of your sexual needs and desire it would be important to remember two things. Never engage in a sexual activity if your partner does not consent and never engage in sexual activity with a partner who is NOT ABLE to give consent.
Another thing to consider is that while it may be unlikely that diseases could be transmitted between humans and animals during sexual activities, it is possible.
It is important to figure out why you decided to do this, and how you can try not to repeat this behavior. It would really benefit you to speak with a professional. If you live in northern NJ, you can get help finding a therapist by calling the Access Center from Atlantic Behavioral Health at (888) 247-1400.