pregnancy symptoms without being pregnant (post partum 3 months)

Hi guys. It’s impossible for me to be pregnant because I’m in a same sex marriage. I am post partum almost three months. I haven’t gotten a period still.. (exclusively formula feeding) but the lethargy is insane. I’m nauseated, I’ve gained weight. I don’t understand and I’m worried. Been trying to make a GYN appt. any insight?