contacts removed from iphone 5

I entered Brenda's number and address onto the contacts app on my iphone. I needed to call her a few weeks later- her number was gone. After hunting around I found it written in an email and re-entered it to contacts, called her and thought that was the problem solved (I actually thought I had imagined entering it in the first place and was loosing my marbles).

So, imagine my irritation when I needed to call her again a few weeks later, and it had vanished once again. Looking through my contact list, it wasn't just Brenda that had gone, actually half my contacts had just been wiped.

Weirdly, though, I managed to find Brenda's complete details in the 'recents' list on my phone- her full name, number & address were all there. Then I found the same was true for my other missing contacts, if I looked in my recent calls or text messages, their info was all there, but it was not saved in contacts anymore.

I've now spent several hours researching, trying to figure out what the issue is, messing with my phone settings, the contacts list on my macbook, icloud etc. and I can't for the life of my understand what is going on.

I just want the contacts list on my phone to be the same as on my computer- if I add or delete any in either place, I want the other one updating. Can someone please help me do this?