This could be an egg, calculi, tumour ect. I recommend a vet trip for some diagnostics as knowing what is going on is the first step to fixing it.
To recall a similiar experience I've had, was with an elder female corn snake. She double clutched, and was super thin. She had had a retained egg the previous clutch which was manually removed after bursting (in itself an emergency). Not long after the second clutch, it looked as if she had another egg. After an unsuccessful endoscopy (she was quite small and our instruments were rather big for the job) an exploratory surgery had a uric acid calculi mass removed. Unfortunately it involved many of the major organs in the area and healing had it's complications. With all that, the calculi came back several months later and blocked fecal movement. The snake, while initially getting better, was suffering and I decided to put her down instead of enduring another surgery.
I hope your snake has a more fruitfull future, good luck 
Ian