jorian,
Coughing, sneezing and/or straining at the bowel increases intrathecal pressure and indeed will exacerbate your symptoms, and has the potential to aggravate and/or worsen the injury.
When you feel a cough or sneeze coming on, if standing, lift one of your knees to waist level and support your ribs with your arms.
Same maneuver works sitting or lying down.
This will decrease intrathecal pressure and provide some lessening of pain.
I hope you feel better daily.
Opiates rock!
Matt