How can I explain without seeming to complain?

I statements. Hard to say for sure without more info, but generically it can help to use "i feel ...." statements rather than "you do ...." statements. This tells the other person you're owning how you feel and is much less likely to put them on the defensive or seem like you're complaining about them. It supports a stance in which you're both on the same team working towards a shared goal.
Communication. State the facts without embellishing the facts. Relate with a calm demeanor and ask for understanding and be open and non-defensive when you are given feedback. Best wishes.