The Sweden striker scored his third goal in as many games during Liverpool's 2-0 win over Ipswich Town on Friday, matching his entire Premier League goal tally from an injury-hit campaign last season.
Liverpool remain unbeaten under manager Andoni Iraola, and Isak believes they must build on their strong start as the schedule becomes more demanding.
"I feel good," Isak told Sky Sports News.
"Obviously, I would have preferred if we had won all of our three games. But we won the last one and we have got to keep going like that."
The striker believes Liverpool can take confidence from the Ipswich performance into their next two matches.
"We've got to use the energy from that game and use it to put in another good performance," Isak said.
Liverpool now turn their attention to the Champions League, with Atletico Madrid visiting Anfield on Wednesday.
The Reds will then return to Premier League action on Saturday when Fulham travel to Anfield, with Isak looking to continue his impressive scoring form.