Am I crazy? Or should I go for it?!

So I’m 21 years of age 22 in January

, I’m a hard worker with a part time job in retail but a full time job at home with 3 kids ( 2 boys and a girl) I have my partner who is also a hard worker and a good provider and a loving father, he is only my daughters dad as she’s my most recent born and the other father don’t wish to know but current partner treats all kids the same he is lovely... but my main question is... should we try for baby number 4 or not? How much more different can 4 be to 3? I love my kids and work hard to provide we are stable in all aspects so suggesters would be grate, many thanks!