After i burst my nearside flexi, i replaced it with a new flexi and bled the brakes but the pedal now feels really spongy, will bleeding the rear solve the problem?

You didn't bleed the rears?

Bleeding order is:

left hand rear
right hand front
right hand rear
left hand front

assuming facing front.

I do but i was feeling lazy today ill do that tommorrow, i know that my rear nearside bleed nipple has sheared so ill have to do something about that.

unless you emptied the master resevoir then a gravity bleed of that corner would have sufficed
remember never to bleed with foot to floor on a car thats done a few miles or the seals in the master cylnder go a lot further than they are used to and can get cut as they return to their normal position (see it as a lip at the top of the bore on a worn engine)
as regards rear nipple sheared ,consider drum off ,pistons held in and bleed via the pipe itself