Do I have to wait to get an IUD while I'm on depo

So I've been on depo for a while and want to change to mirena, but can I get the IUD while I'm still on it? I was gonna change later this month when I'm supposed to get my next shot, but Id rather switch in the middle of September and get the depo shot. My boyfriend is leaving for the air force in September or October and I don't want our last days to be with me having issues with the IUD and having constant bleeding. I'm supposed to get the shot August 22nd, and if he leaves in the middle of September I would like to get it as soon as he leaves. Is this too close to switch?