My DD just turned 2 in April and my DS is 6 months, so they are 18 (almost 19) months apart. I did not plan to have them so close together, and when I found out I was pregnant (when my DD was 10 months), I was overwhelmed and worried about having two under two.
I will say that having two is definitely harder than having one, but you learn how to do it, just like you learned (and are probably still learning, if you're like me) how to be a mom to your daughter. It can be difficult when they both need something at the same time (this happens a lot!), and the little one ends up having to wait for things much more than the first ever had to. It's harder to get out of the house with two, but the older they both get, the easier it becomes. It's all a work in progress. I'm still working on getting a regular schedule that works for both of them...
Even though I hadn't really planned it this way, I think it will be great for my children to be close in age. My daughter didn't understand it at first and had some jealousy, but it passed in about a month. She then ignored him for a few months, but now that he can interact with her more, she is really starting to like him. I can see already that they will be buddies once he can play with her. He enjoys watching her and she makes him laugh (so cute!) and she will bring him toys to play with.
With regards to how pregnancy will affect you, you know best how your body handles it. I had pretty easy pregnancies, but I definitely felt the pregnancy exhaustion more with #2, especially in the last couple of months. I tried to nap when she did and I was lucky that she is pretty good at playing independently much of the time, so she let me lie down near her when I needed to.
If you're feeling like you are ready, I'd say go for it because you never know how long it might take you to get pregnant again. It can be hard having more than one, but you can do it and you won't regret having your little ones close in age.
Best wishes to you and your family.