Its impossible for anyone to tell you whether your pregnant. The best thing you can do it take a pregnancy test, or see your doctor for a blood test. You may need to wait as if you are prgnant you are probably only 3 weeksish. It does seem awfully early to get these symptoms. but you could be so worried your pregnant your mind is giving you symptoms (it happens to alot of people trying for a baby)
Wait for your next period to be due before testing.
And no having a baby wont ruin your plans for the future providing you want them enough – anything is possible!
Good luck