I have to disagree that swearing can be the appropriate way to add emphasis or express feelings.
President Kimball said that "profanity is the effort of a feeble brain to express itself forcibly." If you search lds.org for "swearing" or "profanity," you will find oodles of articles and talks emphasizing the negative impacts of profanity. In a
talk President Hinckley gave in October 1987 General Conference (he was first counselor in the First Presidency at the time), he said the following:
"Conversations I have had with school principals and students lead me to the same conclusion—that even among our young people, there is an evil and growing habit of profanity and the use of foul and filthy language.
I do not hesitate to say that it is wrong, seriously wrong, for any young man ordained to the priesthood of God to be guilty of such."
If it's seriously wrong for any priesthood holder to use profanity, I think it's safe to say it's wrong for women in the church to use profanity, too.
As I was searching for talks/articles about profanity, I came across a Question and Answer in the New Era that had a statement that stuck out to me. I know the Question and Answer section isn't necessarily doctrine, but I thought the statement was pretty poignant. The New Era writer who responded to the question wrote that "Our language reveals who we are, what we think, and what we believe." I know there are people out there who will disagree with me, but like it or not, people will perceive you differently if you swear. It will give a different impression of you to people.
I know that throwing quotes at you won't necessarily make you feel bad enough about swearing to stop doing it, NerdGirl. You have pointed out that you want to feel bad about it, and I think that's a sign that you actually
do feel bad about it, however miniscule those feelings may be. If you didn't feel at least a tiny bit bad about it, you wouldn't be asking us all for help.
That said, I'd encourage you to focus your personal scripture study on profanity. (That just sounds weird, but you know what I mean.) Study in the scriptures and also the words of the prophets and general authorities on lds.org. There's a boatload of articles and talks on profanity on lds.org that you can study. I know you said you've prayed to feel bad about using profanity, but have you prayed to receive a testimony of the importance of not using profanity? Have you fasted about it? You might consider doing that for Fast Sunday this week.
I suggest that even if you haven't fully developed a testimony of why you shouldn't use profanity, keep trying to stop using it. John 7:17 says "If any man will
do his will, he will know of the doctrine-- whether it be of God, or whether I speak of myself." Sometimes we have to act in faith before we receive a witness that something is God's will. Also, avoid watching/listening to/reading media that uses a lot of profanity. If you're taking in a lot of profanity daily, it's going to be hard to quit it, and to feel the Spirit telling you not to.
I hope that wasn't too preachy, NerdGirl. You asked for suggestions and so I gave you some. Hopefully even if it was a bit of an overload, you still were able to pull some useful tidbits out of it. I don't completely understand all the reasons why swearing is bad either, but I know that the prophets and apostles have counseled us not to, and I firmly believe that if you will follow their counsel, you will be able to gain a testimony of this principle.
Also, I am planning on responding to the other part of your question, about the difference between emotion and the Spirit. I've been really busy the last few days, and I wanted to think about it more before I answered it. Rest assured, though, my response is coming.