Adding photos to camera roll

I was trying to upload a photo to a comment and Reddit asked if I want to use selected photos or add all. I chose selected and I added it. Now when I try to add photos to a comment I only have the option of the one. How do I add more photos, when I press the photo icon it gives me a choice of using my camera for a photo just now or the one I originally selected, no option to add more. Help!