My first two are 2 years 3 months, my second and third are 18 months, and my third and fourth are 3 years 7 months.
Don't feel sad! How many months pregnant are you now? Let me just say two...then they'll be 21 months apart, which will most likely give them a very good relationship. You can also pass on toys, clothes, etc. from the older one to the younger one. I know kids are a lot of work and you're still young, but I'm sure that when the baby is born you'll feel happier. It just takes a while to sink in, that's all.