Birth control

I was on the depo shot and I didn't another shot after October and then my bf and I decided I should go back on it so I went to the doctors to get it and they had me get my blood drawn to make sure I wasn't pregnant and they called me with the results and told me it was negative and then asked me when is my next period and I told her I couldn't really say cause it's very irregular like it can be 30 days one month and then 50 days the next month it's never regular so the last time I had a period was last July and the doctor told me I had to come back in in 2 weeks and get another blood test done and then if they comes out negative I can get the shot..so I'm just wondering if that's normal for doctors to do?