Well, whatever people think, just know that they're thinking the exact same thing about me, as well as most of the other posters who have already responded. When I had my FOURTH, my oldest was only just barely 3. So I had FOUR three and under. I did have twins in there, so it wasn't quite bam bam bam bam. But it's still four just the same. My twins were only 5 months old when I got pregnant again. I actually didn't believe it because it seemed the only way I could possibly have been pregnant again was through immaculate conception! When we told my mother-in-law, she actually laughed out loud. People do stupid things, and say even stupider things about issues that are not even their business. Don't even give it a second thought. The worst I've ever had said was "Are they ALL yours?" Mostly it's just something like, "Boy, you have your hands full!" And even then I can see that they are only saying something because they think the kids are cute or something. Most of the time it's not anything negative. You are going to love it, and your kids are going to love having built in playmates. I'm not saying it's all a breeze having kids so close, because it's definitely not. But it definitely is a blessing. Like many have already said, kids come when they're meant to be here. Congratulations on #3. Enjoy it while you can.
On a side note: Do NOT let your husband drop out of school because of financial pressures. My dad did that when he only had one semester left and regretted it ever since. Our family lived pretty poor for our whole lives because of the lower salaries the lack of degree provided. It's just a really bad idea, and even if he 'plans' on going back again later, usually it doesn't happen. It's well worth any sacrifices your family may make for him to finish. Plus, at this young an age, they're going to have no idea whether you're poor or independently wealthy. It will, however, affect them in junior high or high school if they feel like your family is poor. Good luck with everything!