I found another proof of my theorem. Can I present two different proofs in the paper?
If the two proofs are sufficiently different, then it's entirely reasonable to include both of them in your paper.  You might, however, want to think first about whether the proofs might actually lead (easily) to different generalizations of your theorem.  If they do, then you get two benefits: It's then clear that the two proofs are genuinely different. And you have some more general results.