A missed period is the most reliable sign, along with unusual fatigue. Don't waste time guessing based on minor symptoms, just do a home test after a missed day.
For me, extreme fatigue and light cramps were the first signs. But avoid eating heavy sweets thinking it's a craving until you check your blood sugar and confirm.
I felt a strange metallic taste in my mouth and was incredibly tired even before my missed period. It was such an emotional moment when I finally saw those two lines.