I feel unwelcome at work sometimes and think people might be talking about me?

The problem is that you are associating you diminished responsibilities with the idea that they are displeased. You left and came back so while you were gone your duties went to someone else. People gossip no matter where you go and even spread untrue rumors, but if you work hard and are pleasant to others you will gain their trust regardless of gossip. If you know you have put your all into the work, then ignore all of the gossip. It is best to avoid getting an earful even if it is not about you. Focus on your work, and remember you are working for free because you care and others appreciate this.