Why aren't all of my photos on icloud?

I was using icloud on my iphone and been working with them on my pc laptop to upload to a blog. I ran out of space and my iphone would not update. So I turned off the icloud so I could update my phone. I decided to buy more storage and have plenty now. I turned back on my icloud for photos, but not everything is uploading. I only have the last couple of days uploading. I am missing a huge chunk of photos! How do I get it to recognize that and upload them?