The basic principle is that the bleeding experienced by women is menstrual blood, so long as it does not last for more than fifteen days, in which case it is istihaadah (non-menstrual bleeding) according to the majority of fuqaha’. According to some scholars, it is menstrual blood unless it continues for most of the month; if it does that, then it becomes istihaadah.
The menses may be longer or shorter, or it may come early or late. The blood that comes in these cases is regarded as menstrual blood, and there is no need to repeat the fast, according to the more correct of the two scholarly opinions. So your usual period may be seven days, then it increases to ten for example, so the ruling is that it is all menses.
Having a coil inserted usually causes some disruption of the cycle, such as making the period longer, or making it come earlier, or changing the nature of the blood.
What we understand from your question is that the bleeding started after the coil was inserted, two days before Ramadaan, and it has lasted until today (the seventh of Ramadaan), but you did not tell us what your previous cycle was like, or whether the period came at the usual time or not.
Based on this information, the bleeding you are experiencing comes under the heading of menstrual blood, unless it lasts for more than fifteen days, in which case you will be mustahaadah (experiencing istihaadah or non-menstrual bleeding). [According to some scholars, you will not be mustahaadah unless the bleeding lasts for most of a month.]
If it is established that you are mustahaadah, then one of three scenarios must apply:
You previously had a regular cycle, so you should count on your former cycle and refrain from prayer etc. accordingly, then do ghusl and pray. Any bleeding outside of your normal period is istihaadah.
If you did not previously have a regular cycle, then you have to distinguish between types of bleeding: menstrual blood is dark and thick, and has an unpleasant odour, and is usually accompanied by pains (cramps). The blood of istihaadah is light and thin. So your menses is the days when the blood is dark and thick, and the other blood is istihaadah.
If you cannot make this distinction, then you should refrain from praying for six or seven days, because that is the usual length of women’s menses, then do ghusl and pray.
The woman who is mustahaadah may fast, pray and have intercourse, but she must do wudoo’ for every obligatory prayer after the time for it begins, and she may offer whatever naafil prayers she wants to with that wudoo’.
Cases of istihaadah, with evidence, have been discussed in the answer to question no. 68818.
And Allaah knows best.