There is no PNL on spot trading pairs because you are not opening/closing position, you are buing coins. Fliping from one coin to another. Poloniex does not know what's your native currency (USDT, BTC, ADA) so it does not know when you actually open/close your position. 3$ is not enough.
"The minimum trade amount varies depending on the base trading pair and are as follows: BTC, 0.0001
USD (any), 1
TRX, 100
BNB, 0.06
ETH, 0.0001."
https://support.poloniex.com/hc/en-us/articles/360040031373-How-to-Trade


so for some tokens like TRX you will be below the minimum transaction threshold. And trading with this mindset is gambling. And trading with $3 on such a illiquid exchange as Poloniex can bring unexpected returns that will be unreliable and mean nothing. For example, I once had a trading bot that did up to 100% a week on providing liquidity on a small exchange. The math shows that I would have made $500 to $30 million in just 4 months, but the truth was that the bot couldn't make more than $500 a week because the volume was so small regardless of how much capital I put into it.