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.
Manchester United surrendered their advantage to draw 1-1 with Tottenham Hotspur at Old Trafford on Saturday evening, missing the opportunity to claim their second Premier League win of the campaign.
Chelsea bounced back from their defeat before the international break with a convincing 5-1 Premier League victory over Bournemouth at Stamford Bridge, as Jordan Henderson scored his first goals for the club.
Arsenal came from behind to secure a hard-fought 2-1 victory over Leeds United at the Emirates Stadium on Saturday, showing resilience to claim maximum points after falling behind in the second half.
Cole Palmer has signed a one-year contract extension with Chelsea, keeping the England international at Stamford Bridge until 2034.
