I understand because 16 years into being diagnosed with ITP I still look at the bruise and try to work out is it an ITP bruise or is it a result of natural injury. Of which by the way on Christmas Day I happend to bang my knee against the coffee table, something we all do from time to time. Over the 24 hour it came up whopping, the biggest bruise I have seen in a long long time.

Christmas night, the blood blisters were there.... but wouldn't bother ringing then and still wasn't entirely convinced as only had about 3 spots of the rash. Boxing Day, church again with it being sunday. I serve on the Altar and every time I stood or did something I was achey. I felt sure I be in hospital that night, though not entirely convinced.
We came home from church and a quick look at the rash which had developed vagually. A phone call to the ward and was told to go in for the test....
To cut the story short I had a count of 7 this time.
But I have been through plenty of times and the count was normal. Boxing Day was more nervy in that it being Christmas still and if it was up then I be kind of wasting everyones time. So was relieved more ways than one when he came in and told me the count was 7.
But I go through that agonising Is it - aint it. every time and the only thing I would suggest is if in doubt - give them a ring. Learn to rely on instinct too. Whilst that is not scientific, it works pretty well for me. They would get worried if you went through with her every week checking I suppose. But certainly at the beginning they be pretty much okay about it or should be.
I only have to ring up and be there within the hour by car
I don't suppose I have said anything to help ease your worry accept that I do go through that for myself every time I suspect a bruise.
Just keep an eye on them and if you are not happy then ring the number you have and ask for advice and they will say what to do. ITP bruises have a distinct colour, but like I find, injury bruises can be much bigger when platelets are down. It aint guaranteed at all but can be.
hope this helps