Sandra, you have a very unique voice (don't read great) and it might be best and easiest to capitalize on that uniqueness rather than to concentrate on a major voice make-over. I heard Janis Joplin (as well as Louis Armstrong) in your voice and they did passably well, commercially speaking.

I, too, sensed you "poop out" toward the end. Correcting that will only come with time and breath/diaphragm control. You always have your voice with you so sing constantly. You likely have music going through your mind constantly judging from your mastery of the guitar. Now just "voice" those mental melodies any time of day or night.

Breath/diaphragm control can be practiced by singing into a lighted candle. You can see cause and effect of various diaphragm controls. Great practice for any singer. Try different volumes without blowing out the candle. Also excellent for controlling plosives.

All the best to you.