Did they test any urine with a wee stick to test for blood? Squeaking when pooing may indicate a few things including Urine Infection - if so it would need antibiotics to help clear it up, Septrin is often the first choice antibiotic for a UTI, although we have had success with Baytril too... If her bladder is a little inflamed by cystitis as opposed to infection then the Metacam would certainly help as it is a painkiller and anti inflammatory. I would give it till Monday and if she is still crying then go back and ask about a possible infection. As always if it gets worse or she goes downhill get to a vet ASAP. How is she in herself? Eating and drinking okay?
You have some cavy savy vets in Cheshire, details below:
Cheshire Pet
Molly Vagra
Holmes Chapel Clinic
Manor Lane
Holmes Chapel, Cheshire CW4 8AB
01477 544554
Rose Cottage Veterinary Centre
Jen Quayle
Chester Rd
Sutton Weaver, Runcorn
Chershire West and Chester, WA7 3EQ
01928 71758
EDIT: Sorry posted at same time and Helen and Wiebke