I seen too be much more genuine at the beginning of conversations, and I don’t know why. Any suggestions?

I’m a freshman in college right now. All throughout high school and middle school I’ve been pretty shy, but only in the past year or so, my social skills seem to have dropped considerably. I noticed that lately, whenever I get into a conversation with a friend or anyone really, I actually feel like myself and can talk genuinely and crack jokes, but only for a solid five minutes usually before this switch in my head seems to flip and suddenly I become completely different. After this switch, I feel like I just become this chatbot, I only really have generic responses to offer and some of the most obvious or overused jokes are the only ones that come to mind. I have no idea what’s going on, but it’s made it really hard for me to keep up my friendships with old time friends who knew me as a more interesting (imo) person to talk to than how talk today. Does anyone else have this problem? I would live to hear some advice or anything that might help me get out of this rut I got myself into. Thanks!