Pregnant and breastfeeding???!!!

I have a 18 months old and because I’ve been breastfeeding since birth my period never came back. These last few days I’ve been feeling incredibly tired.. absolutely exhausted... I have headaches at night no matter how many hours I sleep. I fall asleep when I’m trying to make him nap and just tired to a point I generally I’m not.. not only that but I’ve been cramping and having lower back pain, not unbearable but enough to not want to get my toddler in my arms too much. Particularly today I’ve been feeling really bloated and just over all not good.. plus I just puked for no reason 😬. I tested a week ago and got a negative but if anything my symptoms have gotten way worse so I don’t know if I’m having pretty bad pms or pregnant and the test just couldn’t pick it up yet. If I am I cant be ober 5 weeks (I was traveling for a month and a half without my husband so no way I got pregnant then).

Question: when do you think I should test again?? I don’t want to keep testing and getting my hopes up and wasting money on pregnancy tests.. but I need to make sure if I am pregnant or not since I suffer from panic disorder and general anxiety disorder that I’m medicated for.. so I need to make sure if that medication is safe for me or not.

So when do you think it would be best to test again to make sure if I am pregnant or not? And until which week can a pregnancy go undetected by a home pregnancy test?? Since my period has never been back I can’t just wait for it to come since I don’t know if it would at all even if I’m not pregnant.