Language interference

Is there anyone that knows or is learning more than one language? I know I am nowhere near fluent level or polyglot in the languages I do learn, however I am starting to feel the language interference! Does that happen a lot? I start off a sentence in one language but then in walks the other language and I confuse a lot of people including myself and my Spanish and Korean teachers >.< As Spanish has to be the most important at the moment, I really can not risk letting Korean or English in my case take over. My tongue can not resist the temptation to speak those two languages at times even though I know in my mind I must speak Spanish.
Today I surprised my Spanish teacher when I answered her in whatever French I remember! Well...I have a very important Spanish test coming out so time to drench myself in the lovely español. Will return to blog soon and edit some very important pages. Reader, stay well until then at least.