2007 Lexus IS350 hesitant to start

[Charissa]

Hey team, 

I brought a 2007 Lexus is350 5 months ago and about 3 weeks ago it started making a really strange noise when I started it, then it would go away. A week ago I went to turn it on and it didn't start. It was trying but wouldn't spark. Took it to a mechanic who said it was a fuel pump and replaced it but since I've had it back it's been really hesitant to start. Sometimes it starts fine others it's trying and trying then last second it sparks. Could it still be the fuel pump? He also ran a diagnostic on it and everything showed up as normal. Appreciate any help!