Since winning 3-1 at Liverpool on December 15, Villa have suffered three heavy defeats in a row, conceding a total of 15 goals and failing to score once themselves.
Lambert said: "The last three results have certainly hurt us.
"Everyone was positive after the Liverpool win but there is now a negativity after these three defeats.
"I understand that feeling but I have a belief that Aston Villa will be fine. The big disappointment is that there are a lot of experienced players out of the team.
"Andreas Weimann had to play at the last minute against Wigan despite having a leg injury. Once we get everyone back in January we will have to wait and see what happens.
"We had a decent spell in the first half when we looked like ourselves. We had a couple of half chances but in the second half there was no creativity. That was hard to take for sure."