YOU SAID:
I wore Swimming trunks under my trousers all day
INTO JAPANESE
私は一日中私のズボンの下に水泳パンツを着ていた
BACK INTO ENGLISH
I wore swimming pants under my pants all day
INTO JAPANESE
私は一日中私のズボンの下に水泳パンツをかぶっていた
BACK INTO ENGLISH
I was wearing swimming shorts under my pants all day
INTO JAPANESE
私は一日中私のズボンの下に水泳パンツを着ていました
BACK INTO ENGLISH
I wore swimming pants under my pants all day
INTO JAPANESE
私は一日中私のズボンの下に水泳パンツをかぶっていた
BACK INTO ENGLISH
I was wearing swimming shorts under my pants all day
INTO JAPANESE
私は一日中私のズボンの下に水泳パンツを着ていました
it is unlikely that this phrase will ever reach equilibrium