Possible rear tyre puncture

Noticed the other day my rear tyre felt a bit low, hadn't filled it up in a couple of weeks but after filling it up I noticed 2 shards of metal embedded in the center a few inches apart. It's been 5 days since I filled the rear tyre up and the pressure hasn't gone down even after roughly 100+ miles.

Now I already have a plug in the tyre and have been told that I cannot have 3 so if one of the pieces of metal has punctured the tyre I can get it fixed but if both have then I need a new tyre. This one still has over 3000 miles left so I'd rather not have to replace it considering another RoadSmart is £140 fitted.

Anyone know where I can get a new RoadSmart for less than £120? (the extra £20 is fitting)

A little peed of at the moment.

just put some puncture safe/ultaseal in it it always works for me,about £24 to do 2 tyres and lasts the life of the tyre and tested up to 150 mph,and its the stuff the post office use in there vans