A.M.
Girl!! Do you love chaos or what???!!! you want 3 kids all under 3 and a new puppy!!??? and I'm guessing the puppy's not potty-trained either, huh? yikes!
Please examine and put a high importance on your sanity level with all this chaos while having an absent Dad who travels a lot for work. I mean, you're almost a single mom with that kind of business traveling. And btw, boys take longer to potty-train than girls do. {if even he's already showing signs of wanting to go on the potty...it can still take a year before he's on his own and reliable...i've seen this soo many times with many boys...the interest will come and go.}
You must take care of MOM! Your kids need and deserve a sane, well-balanced, well-rested mommy! And you deserve it, too!
I'd at least wait until the boy is 2 1/2 before thinking about conceiving. So much can happen and can yet to be discovered with boys under 2....(speech delays, austism spectrum, behavioral delays, etc.). I've seen couples jump into the 2nd baby thing like it was getting a new puppy only to find out they wish they'd waited because they discovered their first born was still growing and developing and needed more attention now (diagnosis of autism doesn't always happen until after 2 -- and there's a big wide spectrum of behaviors of autism).
Devote all your time and attention to your 3 yo and your 18 mo...they are still growing and need Mom's attention. They are still so young!