Frank said: "It's always irritating or frustrating to lose a match. That's the most difficult thing in this business.
"It was a very even match between two teams who neutralised each other. There wasn't much in it. We had the biggest chance through Ivan.
"It's very irritating they scored from a second phase. Even game, should have been 0-0 in my opinion. A little bit boring.
"Right now I'm just irritated we lost a match. It's been a tough season. It's always been our aim to finish as high as possible and be an asset to the Premier League. It's important we finish well and keep the momentum into last season.
"As a team we played average. Not many players stood out. Our front three weren't at their best. It was a starting point for Ivan and he'll be better next time."