iPhone 6 wouldn't save photos to device

Recently when I tried to send a photo through messages, it always have a little pie like a loading sign located at the corner of the photo. Sometimes it won't load if I am getting bad signal strength. I am using an iPhone 6 and I have iCloud Photo Library on. I tried selecting download and keep original option but it never downloads the photo. Every time I open up "photo" it just shows me a bunch of blanks with a cloud symbol located at the bottom right corner. I am trying to keep the pictures on my device so that I don't need internet to look at my pictures. Every time i turn off "iCloud Photo Library", it deletes all my pictures. I tried backing it up and restoring it but it still doesn't work. I have GB worth of pictures and GB of space. This has been bugging me for a long time and hope I can get answers to fix this.