Why did my thai curry have a bitter aftertaste?

I'm on the low fodmap diet so i tried making my own thai curry paste (without shallots or garlic). Here are the ingredients that i used:

*1/4 cup coriander leaves, stems and roots *1/2 tsp black pepper *1 tsp coriander seeds *1 tsp cumin seeds *1 large stalk lemon grass *6 red chillies *1.5 tbsp ginger *1 tsp salt *1/4 spring onions *3 tsp garlic infused sesame oil *1 tsp lime juice

I'm guessing it's either the lemon grass or the lime juice which made it bitter

btw, does anyone have a good low fodmap thai curry paste recipe? I've tried many and have had no luck finding one that resembles an authentic thai curry