Lamps struck from the spot in their 1-1 draw with Fulham.
Asked how it felt to reach another milestone, Lampard said: "Not too good at the minute. It feels like a little bit of a loss."
The 33-year-old, who has scored more than one landmark goal this season, added: "They'll be nice when I look back and I'm an old man.
"But I just can't enjoy them after we didn't get the three points.
"I'm pleased to try to help the team and score goals. Landmarks are great.
"But, at the present time and with the position we're in in the league, every league game is a final for us and we want to be winning them."