Period during breastfeeding

Rabab

I'm 40 years old.

my period came after 40 days of my giving birth it was almost regular until last month between 29 and 35 days ، but it's too late this months today is CD 38 snd i already took a pregnancy test snd it eas negative otherwise I have a pregnancy symptoms lik dizzy, nausea, cramps,back aches and feeling tired . really I'm so confused .any one had a same experience ?