The Lions began the season with six games without a win, then picked up three straight victories to lift themselves off the foot of the table.
But they were thumped 4-0 at Birmingham last midweek and then went down 5-2 at Bournemouth on Saturday.
"You expect to come under pressure in games in this league but you have to defend them," said Lomas.
"It just all went massively wrong for us after half-time.
"After three great performances and wins it's hugely disappointing to lose the last two games the way that we have done, particularly conceding nine goals in them."