I have 4 children, the first and second are 3 years apart, my second and third are just one day shy of being exactly 2 years apart, and there is 5 years between my third and fourth. There are definite pros and cons to having your children close together, and also in having them further apart. I would say that if both you and your husband feel ready to bring another child into your family then that is up to the two of you, and has nothing to do with your extended family (unless you are relying on one of them for childcare).
For me personally, the hardest part of having two close in age is changing two diapers instead of one. And that really isn't hard as much as it is tedious. My two boys are really close, and although they fight, they are still eachother's best friend, and will always have a playmate. I don't regret having them close together at all. The benefit I see in waiting a little longer is that your daughter is your only child right now, and it is always great to spend as much quality one on one time with her as you can. This will be her only opportunity to have mommy and daddy all to herself.
Since you are still young, and it sounds as if you have a family who is not afraid to voice their opinions on what you should or should not do, you might find yourself doubting your own instincts and leaning toward the advice of your parents. With that said, only you and your hubby can make the decision that is right for your family. And if you are still really unsure, prayer is a great way to gain insight and wisdom. God always knows what is best for us, even when we don't! :o) Best wishes to you, your hubby, and your little girl!