Period is normal, on time for last 8 months. I had tiny amount of spotting week ago, then nothing. Pms symptoms still. Why would it stop suddenly?

various possibilitie. There are various possibilities... Pregnancy or ectopic pregnancy still may be present ( if sexually active), stress, medications, or other illnesses that effect hormone levels could lead to the presence of spotting instead of a normal period. You might call your primary care provider this week for a follow up apt.