Despite Port Vale going down to ten men in the first half, Hereford United failed to score this afternoon and conceded two 'easy' goals.
"I'm very disappointed with the result," Trewick told BBC Hereford and Worcester.
"We conceded what for me was a very straight-forward type of goal which we should have been defended better after ten minutes and that gave the opposition a lift.
"It's a common symptom of matches recently where we've lost narrowly and the goal the oppostion have got, they haven't had to work too hard for.
"We had a few chances - when your chances come you've got to take them."
Vale's second goal came after Constantine lost possession in the Vale half with nearly all the Bulls player well forward.
"Later on in the game you have always got to be careful when you commit people forward - when you start chashing things you are always vunerable.
"But 2-0 or 1-0 it doesn't make any difference as you lose the game."
Ryan Valentine's sending-off:
"I think it's difficult for referees to pick out one individual unless he said something which I not aware of.
"I thought the tackle was a decent tackle. I thought he won the ball. I need to look at that."
New loan player Lateef Elford-Alliyu (pictured) made his debut for the Bulls:
"He did some decent things. It was hard for the lad because we never established a position in the game where we could really go on and be comfortable.
"He did okay, he's only young, he's got talent and he played his part."
And new players:
"I'm hopeful I'll bring in someone before the deadline on Monday."