Hi Jjiillee,
From my experience with my 3.5 year old, ITP doesn't appear to cause high fevers; both my kids - including the non-ITP one - have had fevers that high. From the reading I did about ITP there doesn't seem to be any connection between the two.
Again from my experience, viral infections can lower the platelet count significantly.
Tommy complains about stomach pain fairly regularly, he has had a few tests, but nothing came out of it. Some recent literature suggests that, in a few cases, H. Pilory (a stomach bacteria) may have something to do with ITP. This can be tested with a stool sample.
I'd certainly call your doctor if you're concerned.
Hope this helps,
Daniel
BTW: I wouldn't worry too much about a possible temporary drop in platelet counts. Certainly not when your kid is in bed being sick