BFN 😩

I've been breast feeding my 18 month old and I got my period back last month (July 20th). I have been trying to conceive and my period has not came, I took two pregnancy test and a lab test at a women's care Center and their all negative with no faint lines. I have severe cramping, sore nipples when breastfeeding and a little nausea with lots of white and clear discharge (mostly clear) I've been told it's all in my head and that my period is just going to be irregular for a while until I stop breastfeeding.

Please note:

I breastfed my first child for 23 months and my period came back at 18 months and was regular every month until I was pregnant again five months later.

I've never taken a pregnancy test and got a negative, I only took test when I absolutely knew I was pregnant so these tests are really shocking me because I have all the symptoms