Is there a term for this? Is there anything I can do about it?

Aphasia is the clinical term for not being able to say what you mean (only in severe cases), but, needless to say, you don't need a suspected diagnosis in order to see a therapist. In fact, most therapists I know (especially ones who aren't psychiatrists, but are psychologists) are nondiagnostic and mostly just talk, instead of giving diagnoses, so explaining your problem and just saying what you said on here should be good enough. I'm not sure what you mean by open-ended questions, but I think talking to someone when you are having problems is always a good idea. I hope you work things out! :)