I did kind of the same thing -- I got pregnant with my daughter when my son was 18 mos. I started really yearning for another baby around the time my son turned 1. I don't know if it's just nostalgia for the baby days or what, but I couldn't wait to get pregnant again. It is sometimes tough with 2 (mine are 24 months apart -- dd was born 2 weeks after ds turned 2 years old) but I don't regret it. I am glad to have them close together. My husband works a lot and occassionally travels, so the kids and I are a tight little unit. I'm currently 36, so that was probably part of my motivation for having 2 so close together. Also, if I decide to, there's still time for 1 more (although I'm pretty sure we're done).
I'll tell you what totally saves me -- wearing the baby in a sling. When I go out anywhere, I wear the baby in a sling and then I can put the 2 year old in a shopping cart or in a stroller if I have to. I can also have the baby in the sling and still chase my son around the park.
It has been a little hard on my son, but mostly he loves his sister. Just a little jealousy when I nurse her and he wants "mommy cuddles". It wasn't a financial strain at all since we had all the gear from the first child. I did buy some clothes, but I was able to re-use all the gender neutral newborn stuff. Some relatives did send us clothes as gifts, too. The extra diaper expense is a hassle, but my son is now really close to being potty trained so that should be over soon.