Confidence issues...?

Im really outgoing and can be really funny when im with people that i know and im not the least bit shy ask annyonee. But idk whenever i go to tennis practice i like shut down. Like i feel that people are critisizing everything i say and i feel intimidated which theres no reason to and do so i dont say anything all practice and i dont like it. Like i feel that if i say something or cant think of a witty comeback fast enough that ill look or sound stupid and i get really self consious. Its the same thing with guys like i can get them interested and stuff but then after that its done like im no longer spontaneous or anything because i feel like what i say is dumb and theyll get turned off to me (not like that lol) and i dont know what to do. I feel like its keeping me from having a boyfriend or being one of those people that people love to be aroundd. Help..? :/