I'd like to make my own Merchandise?

the only thing I'm wondering is I'm a huge Anime fan. I draw lots of different Anime my Question is If I drew something myself whether it be from an Anime, Cartoon, Band, or anything would/could I be charged with Copyright infringement? I see many different people on sites like Tumblr or DeviantART selling shirts they made with a Design they did using things based off a show or anime they saw so why aren't they being charged? is it ok I'd like to know before I get into this cause I really would love to make this into a Job. making good Anime and TV show shirts that Don't look stupid like a lot of others I've seen let me know what you think thank you~ please no ignorant comments...