I think your holes are plugged with chemical deposits. At the end of the sprinkler, the opposite end of where the hose connects to the sprinkler, there is a needle plug that you can un screw. It's black. This tool is designed for cleaning the holes. Best and Happy Yardening, Nancy.
How To UnStick A Dramm Oscillating Sprinkler
Question From: P. Hill - MICHIGAN
Q: Nancy, I purchased a new Dramm oscillating sprinkler this summer to replace last year's Nelson oscillating sprinkler which was always stuck. My new Dramm worked well for a while and then it also got stuck. We are in Franklin on well water...I soaked it in Ironout, to no avail. Otherwise, I love the sprinkler. Am wondering if you might have had the same problem and found any solutions. I like to use the oscillating overhead sprinkler in my beds.