We have a sweet male labrador, approximately 9 years old. A few months ago he  started excreting loose bloody stool. It wasn’t consistent but became more  frequent over time and in addition to blood, mucus was present in the loose  stool. We noticed his anal glands terribly swollen.  
The vet checked and stated he had developed an infection most likely from the  blood and irritation. The blood and mucus was excessive at this point. He was  put on antibiotics and they also performed a biopsy which came back  inconclusive- blood counts were fine. The swelling eventually went down.
The vet was unsure what to make of the situation. Would an x-ray be able to  help shed light on what might be ailing him? 
He exhibits no discomfort and his appetite and demeanor are normal. He  continues to squat frequently with visible strain but little comes out, just  drops of loose stool with blood. 
Our vet urges us to go to a specialist for further testing but our plan does  not cover these costs. We are struggling to figure out what our next step should  be.
HELP!!!!!! 
Thank You!