I've got 3 kids and had a miscarraige a year ago. Since we've been trying for a baby but nothing, is there something wrong with me?

Finding out if you have lost the ability to conceive or carry a baby to term is usually very expensive. So unless you can afford a fertility expert, I would treasure the children you have and count your blessings. (I assume that the same man fathered the 3 you have? If not, it could be the man, and both of you would be tested.)