It is the nature of 7th chords that they sound odd. A 7th chord has 4 notes one of them is a major interval and one is a minor interval. 7th are used alot in Rock and Blues. When I first tried to play them I didn't like the sound. However as my musical pallette grew I started to appreciate them. I had to develop new sensiblities about harmony and then make those a part of how I approached music. I now find them irriplacable and use them all the time.

As long as your guitar is tuned properly, I would suggest you start using 7th so as to develop a broader sence of harmonic structure. It will add a blusy sound to your playing. Once you do that, you will start to enjoy 7ths.