my menstral cycle is usually three days long and this time it lasted three days and on the fourth day I didn't bleed all day and then randomly I had a gush of blood and I bleed for like two hours then on the fifth day the same thing happened I didn't bleed all day and then randomly I just started bleeding and it lasted the same length of time and I'm not sure if I should be concerned or not..

I don't think you need to be concerned, you maybe just had a heavier flow than you usually would. Its not uncommon to stop your periods even for 3 days only for it to start again for a day or two.

I have the Mirena IUD, with some issues.

Have been bleeding on and off for a month. Start bleeding durning sex

Having on and off bleeding for a month . Bleeding durning inter course

I would say at this point its nothing to be concerned about... however if you notice it has lasted 8 days or feel any sudden pain I would go in asap, could be an early ectopic. But Regular periods can start up again if you did any heavy lifting that day or increased activity. Try to take it easy for a day or two and see a dr if it is persistent!