IPhone says storage is full when it shouldn't be?

So I got an IPhone 6 in December and I remember like after a week getting a notification that I couldn't take anymore pictures because I was out of storage room. I found this odd since at this point I had less than 40 photos and less like five very short videos and I didn't have nearly enough other data to make my storage not allow for more photos. After a wile the message stopped popping up but recently it's been doing it again. It tells me that 150 photos and 10 short videos takes up 3.6 G on my phone. I saved all the photos and then deleted 150 photos and videos and it still tells me that i'm using 3.6 G of space. Anyone else had this problem recently? I've been meaning to go into the apple store but it's a bit of a hassle so I was hoping someone had an explanation or some kind of solution. Thanks

Added (1). I kind figured it out/found a temporary fix. My phone was keeping a ton of photos in the recently deleted folder around for a long time (it does this to give me an opportunity to recover them if I waned them back. There was like 550 photos and videos in there which still really doesn't add up to 3.6 G in my opinion, but either way, when I overrided the delay for deletion my storage went way down so, thanks anyway)

Even when we delete things, your phone keeps fragments. Download.com ( I think - or another tech mag) has good hints this month on how to trick you phone to CLEAN OUT all those hidden things

You could have too many apps. That takes up some data, especially if its an app like Clash Royale or something.