17 U.S. Code § 107, which governs fair use in the US, says (emphasis mine):
Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include—
(1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of the copyrighted work.
The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.
Note that commercial/educational use is part of only one factor. Even if that factor is in your favor, it may not be fair use, and even if it isn't in your favor, it might be fair use. Because fair use is determined on a case-by-case basis, we can't really say whether your use is fair use, with or without the donations. That would be the sort of thing you'd ask a lawyer about to get real legal advice on your particular case.