Town won 2-1 at the Galpharm Stadium on Saturday but Clark was far from satisfied with the overall teaam performance.
"I can't use the weather as an excuse. Southend have gone even longer without a game yet they looked brighter than us," he said after the match.
"In the first half we were average at best for about 10 minutes and poor for the rest of it. There was no spark and, while we improved a bit after the break, I'm disappointed with the standard of that performance.
"But there have been times when we've played really well and got nothing. I think I'd rather have the points than the plaudits."
"I was particularly disappointed with their goal. It was sloppy from our point of view.
"We need to keep more clean sheets."