Jermaine Easter equalised but goals from Jermaine Beckford and Andre Moritz won it for the Trotters.
Lomas said: "We were bitterly disappointed about the first goal. It was a clear head knock.
"It's the first head knock of the season that I've seen that the game has then played on and Nicky's a very important player for us in that situation because he plays in the centre of midfield.
"The referee said his microphone wasn't working because the fourth official was telling him in his microphone that it was a head knock.
"We seem to be getting the short end of the stick with decisions lately and we could have had a couple of penalty shouts there as well."
The Lions have now gone five games without a win and are just three points clear of the relegation zone and Lomas wants to see more defensive resolve from his side.
He added: "We showed resilience to get back in the game but we shot ourselves in the foot conceding that goal just before half-time.
"We're not far away but we need to tighten up at the back or you're not going to pick up results in games like this."