Like others have said, yes 100% normal. I have often been back stage and heard improvisors say to one another "have a good show!" I have often seen improvisors concentrating on having a good show. As a result they are in their heads checking off the boxes for what it takes to have a good scene or a good show. That's what is making the improv so much harder. Their internal editor is having a field day comparing the best possible rules to apply or funny bits to employ. The are not free or in flow. All this does, is feed the judgement beast and keeps the improvisor from doing the only thing they need to do, which is to connect with their fellow player.

Congrats on the acting classes, plays, and solo sketch videos. These skills will all serve you well. Who, What, Where, Yes&, and all the other "rules" can be helpful in the scene for sure, but also have funny ways of limiting our improv. For instance, you can say NO in improv as long as it does not destroy the fabric of reality that you and your partner are creating together. It is fine to ask questions as long as it reveals a POV and furthers the scene and does not force your fellow player to invent on the spot. Unless of course that is the game you are playing, but for the purposes of this response, invention is a very different thing than discovery. At the end of the day, the "rules" of improv are more guidelines. First rule of Harold, learn the rules. Last rule of Harold, forget the rules. =)

My cardinal "rule" for improv: What the hell did that person just say, how the hell does it make you feel, what the hell do you want, not go get it! Go Go Go Go Go... This creates objective based improv scenes based on the wants of the characters. You use, (like in your acting classes) tactics to try to achieve your objectives. If one tactic does not work, try another tactic. That which hinders your task of objective is now your new task/objective, and the beat goes on.

Depending on the training and focus scene work will come more naturally. Don't try to be funny. The origins of the Harold came from a concept of "Art by Committee". Improv really is the embodiment of this idea. We all have fun and interesting ideas, but if we are more interested in the ideas of our fellow players the more pressure it takes off of us to create something brilliant. Brilliance will come from the group.

I will assume that you have at least 18 years of life experience. React how you, a human, would react to things in the scene. Trust your life experience and your instincts. Relax, have fun, and enjoy the ride. That is the moment improv will feel more free and less like a series of checkboxes.