Herd, who turned 20 on Monday, started three successive games before being forced off with a hip problem during the 3-2 win at Brighton last month.
Since then, Herd has lost his place in the starting line-up to George Friend, who is on loan at Roots Hall for a month from Wolves.
"It's been frustrating for me, especially as I came out of the team because of injury," he told the Southend Echo. "Things had been going well because we drew 0-0 with Leeds which was a good result and then beat Leyton Orient 3-0.
"But against Brighton I got an impact injury and although I tried to carry on I had to come off during the second half.
"It's disappointing but these things happen in football and you just have to get on with it and wait for another chance."