Issue selecting text on iPhone

Hi. On my iphone I can't select text I've already written. I can double tap words and all it does is bring up a menu for where the cursor already is. Also tapping the screen to move my cursor doesn't work, it just brings up the menu like I said. Holding the screen to bring up the magnifying glass to move the cursor does work but that can be temperamental at times too. The forum is still useable but it is a bit irritating. Just thought you'd want to know

 

Sorry, maybe a bad use of words. Type a sentence and then put a full stop just like I have now. Now without holding the screen to get up the magnify, move the cursor to somewhere else as if you were trying to correct a spelling mistake or something. The cursor won't move just by tapping. It could be because I haven't made the switch to iOS8 yet, but it does work on other forums. Also I'm on an iphone5 but I doubt that matters

Cheers