Low milk supply

Ni

Can anyone tell me how I can identify if I have low milk supply? My 4.5 month old is crying a lot since past 2 days. She gets a bit settled once she comes in my arms or she moves about in someone’s arms. She puts herself to sleep while feeding. She’s exclusively bf. She has enough wet diapers as she has always had and her soft spot isn’t depressed. but someone got me to think that she might be hungry all the time because my supply may have been reduced. Anyone know some good indicators plz?