Late period post partum

So I had my daughter 3 months ago. I haven't breastfed except for the first couple weeks. I had a period last month starting on the 4th, it lasted 7 days. So by my pre pregancy cycle I should have started on the first. I figured it could be a little late, but we're going on 10 days late now. I know it can take awhile for your periods to start again, but once they start shouldn't they just kick right back in?