More than one can handle with

荷(に)が重(おも)い describes a responsibility that exceeds someone’s ability or experience. Literally, “the load is heavy”.

Dictionary Definition

力量(りきりょう)にくらべて、負担(ふたん)や責任(せきにん)が大(おお)き過(す)ぎる。

The burden and responsibility are too great compared to the degree of ability to get things done.

Goo Dictionary

Examples

Too much to handle on top of class representative duties with 荷が重い

Manga panel from orange showing example of Too much to handle on top of class representative duties with 荷が重い.
orange » Volume 3 » Page 121

Takako and Azu tell their teacher they want to participate in the sports day relay race. The teacher points out that participants have already been decided, then one of the decided participants chimes in.

生徒(せいと):
「私(わたし)もクラス代表(だいひょう)はちょっと荷(に)が重(おも)いなと思(おも)っていたので…」
“I was also thinking I have too much on my plate as class representative.”
「できれば代(か)わってもらえたら嬉(うれ)しいです」
“I'd be happy if I could switch out.”