Can chronic infection cause lower platelet counts? and once treated, could that cause platelets to return to a more normal range?

Maybe.: That may be true. Depends on a lot of things, inc. the cause of infection. Often platelet counts might have been low before an infection, but were not tested recently and so the finding may not be due to the infection at all. There are also other causes of low platelets. Ask your doc what the plan is to follow up on these. Repeating the test to follow it after a week or two is reasonable.