While Mercedes team-mate Valtteri Bottas produced a brilliant performance to secure his maiden F1 win at Sochi, Hamilton struggled with a lack of balance and an overheating car in fourth place.
The situation is further complicated by the fact that the two Mercedes were running similar set-ups.
"I can't explain it right now, but I will do some work over this week to fully understand it," said Hamilton.
"I have some theories about how it felt in the race and qualifying, some ideas, but lots of work will be done to figure it out."
Although Hamilton made a good start to challenge Kimi Raikkonen on the run down to Turn 2, he lost momentum as he got boxed in behind Sebastian Vettel under braking.
That kept him in fourth and, with his performance then further hampered by the need to cool the engine as he followed the Ferrari, Hamilton said from very early on in the race the chance of a podium was gone.
"From lap five onwards I just had to slow down and stay in fourth," he said.
"There was lots of turning down of the settings and the unit. I had cutting of one of the cylinders because of the temperatures.
"I was going to be fourth from very early on.
"I was slow from [Saturday] so that doesn't really change.
Read the full article on eurosport.co.uk: Lewis Hamilton: I can’t explain my poor pace in Russia