Get eyes checked at local opto. It may be eye strain, weakness in one eye or something. At 2.5 a local opto should be able to say if anything is "off" and perhaps give you a referral to a paed opthamologist. It's probably nothing at all, but I'd always err on the side of caution and get checked. Could just be dry eyes due to heating etc. but always best to play it safe and get checked. We have had dd on six mintky eye checks for pretty much her whole life due to family history and a turn she had as a teeny bub. Both local opto and the opthamologist have been awesome with her