bruised toe pads!

Hello,

Maybe this has come up before but as I'm a complete luddite I can't find it.

I'm getting up to the 6 mile mark (for the first time) now but ... on anything over 5 miles the pads of my toes are really hurting - both feet. They feel like they are bruised and I have to try and run on my heels a bit more.  Once I stop for 10 mins they are fine for walking and don't hurt and don't look brusied.

 I have good socks and good proper running / not too old trainers. 

I also get the same when I walk for a long time (say up Snowdon or some such).  Again I've got all the right gear.

 Can anyone suggest a fix?! 

 I'd really like to get up to a half marathon @ some point.

 Thanks in advance.