iPhone issues with storage, keeps getting smaller

So, I used to be able to take 6-700 pics on my iPhone before it would fill up and say I couldn't take anymore. I've had the phone for about a year and a half now and every time I import them and delete them with photo stream, i can take less and less the next time. Now i can only take about 75 pics before it says i have no room left. I haven't added many apps and even have deleted a bunch to try and help. I download about one every 3 months and usually delete one about as often. It's really starting to piss me off. Any ideas?