Ttc to soon?

Hi everyone! My youngest just turned 4mths today! And I cant stop thinking about having another one! My depo just ran out and with the other 3 using the depo for 4yrs with each It's taken no longer then 4mths to get prego this time i only got 1shot so I hope it happens even sooner! It would be our 4th! Is anyone else TTC or has TTC so soon?