Hello All! THANKYOU in advance for any help/advice.

I'm writing re: my 2 yr old son. Quick history, a month ago I took him to the Dr's for numerous symptoms including random fevers, fatigue, shortness of breath, and complaints about leg/foot pain that occasionally made him limp or refuse to walk.
The Dr. said he thought he had a sinus infection and prescribed antibiotics, but also noted his super pale "ill" appearance and ran a cbc. His counts were normal, WBC was 12,700, platelets were 360,000, but he was anemic. SO, he said to give him extra iron supplements every day and re-test in 2 weeks. At the next CBC, he was still anemic, WBC were 14,000 and platelets had dropped to 200,000. His MPV has also been flagged as low on each test.
He said to continue the iron, and he goes back for another CBC in 2 more weeks.
I'm just wondering if the drop in platelets in 2 weeks is totally normal? Or could it be a sign of something?
I do have to admit, the iron seems to be helping his extreme fatigue and sleepiness a bit, but the leg/foot complaints have not stopped, and now he also complains about his wrists.
I think I'm just being a worried mommy, but I would really appreciate advice about the platelet drop! THANKYOU~