Weird spotting?

I got a copper IUD put in in October 2013, and my periods were heavier and painful for a while but had settled by the new year. 
I've been having sex without a condom and just relying on the IUD for about six months now, and in the last two my body had been acting up. Oddly enough in the last two I haven't even been having sex, as my boyfriend hasn't been here! 
Between my July and August period I had about five days of spotting! I didn't note the dates (silly) and I told the doctor the next time I seen her and she said to note it if it happened again. 
My period in July was between the 13th and 19th, and my period for August didn't start until the 22nd. That's a long gap, I'm usually about 30 days average between them. 
The spotting has happened again this month, from the 5th to the 9th. Glow is estimating my period is in six days, but I won't be surprised if it is late again 😔
I recently had smear and STI tests and everything came back clear. I'm definitely not pregnant as I said, my boyfriend has been away visiting his family and just came back this week, as well as various negative tests from late period panic. 
I'm going to see a doctor again ASAP but I've just moved and need to re register and a new practice and I'm not sure how long that will take.  Is this a major concern? Has anyone else experienced this? I'm panicking a little sorry for the wall of text!