Part Time Job 's Boss doesnt understand

I am so stress and not sure what to do becoz I have migraine history and whenever I am pregnant, it will come more often and the thing is it doesnt "notify" me in advance . It comes anytime . I had work schedule ytd but about 4hr before i start my work, i felt dizzy and have some migraine aura . So i told my boss that I wouldnt be able to work . It maybe v last minute but I cant risk anything since I felt dizzy esp . But he , not being understanding, reprimanded me in the group chat . I am not sure what to do. He even say " This is the last chance , one more time , I'll fire u or u quit urself" This is my first time that I really cant go to work . The other time when I felt v sick , I told him , but in the end I went to work because nobody wants to help to take my shift and the boss heartlessly says " find ur replacement urself " Now I feel so stress because I really not sure what to do .