3 Constipated G Pigs!

Question
Dear Anngela,
I have 3 female G Pigs (1 short hair & a mother & daughter long hair), approx 1 year old. Problems began about 5 mo ago, when 1 had blood in urine & painful urination. Vet diagnosed her w/cystitis & gave bactrim, although he didn't do exam or hardly look at her. Within a few days the other 2 came down w/same thing, but the bactrim seemed to help.
Since then, all 3 have recurrent problems w/ stomach becoming full(almost as if pregnant) & what I believe to be grit (but no blood). When 1 gets it, within a week or so, the other 2 will too. I use mineral oil & gently rub grit away & will give a little mineral oil if constipated.
About 10 days ago, the short hair GP began whimpering & stomach was full.  Within a week the other 2 had it too. No grit & did not respond to mineral oil, so took short hair to vet (not same vet) & vet was not sure, but thought perhaps gas & gave Metronidazole (enough for all 3). That was 2 days ago, but I stopped giving the medicine because the constipation worstened. Currently all are bloated, very constipated & miserable. Mineral oil no help, tried a bath w/ soapy warm water, but still no poop! It would seem diet was cultprit, but I feed Timothy pellets (for last 5 months), timothy hay, & small assortment of greens.
This is worse round yet & I'm getting nervous. Any idea what coiuld be causing this?  Thank you very much.  

Answer
Hi Pat.  Although I can't explain the painful urination or bloody urine.  But since you didn't mention it this time I am going to leave that part alone.  Sounds like internal parasites to me.  Just like in puppies, when their stomach gets very bloated looking and they have defecation issues a lot of times its internal parasites.  The medicine for dogs/cats is called "drontal."  Its not cheap, around $13 per pill (I wouldn't imagine you'd need more than a few) and you'd probably have to get it from a vet to get the right dosage.  I know some pet stores sell it over the counter, but you'll have no idea on dose and to be honest I've never used it on guinea pigs.  Ask a vet about it, because it is possible they are allergic.  Penicillin will kill guinea pigs. But it strongly sounds like internal parasites to me, aside from the urine issues.  The only thing is with internal parasites, usually the stool is soft not the other way around.  Try a dewormer of some kind, call an exotics vet to find out what would be best to use, "drontal" is what is best for the dogs.  I hope this helps, there is a pretty decent exotic vet in Indianapolis I can give you the # for if you want to call long distance for advise.  
Anngela