(一).I'm under a lot off pressure.我的壓力很大a /我覺得負擔很重。
This expresses that "I'm feeling very stressed." Usually people have this feeling when they have a lot of extra work to do.
put (a lot of) pressure on 給......施加（很多）壓力
I'm under the gun.我備受壓力的煎熬。
原音重現：

A: I'm under a lot of pressure at work.
我工作的壓力很大。
B: Oh? Do you have to work on an important project?

哦？是嗎？你在做一個重要的項目？

(二).It Couldn't have been easy. (對你而言）不是容易的事兒。
This expresses that "It must've been hard for you." The speaker thinks a person had a hard time with something.
It hasn't been easy.不容易。
Things haven't been easy.(雖然我克服了 困難并取得了最終的勝利，但）很不容易。
原音重現：
A: How did John become so rich?
約翰是怎么變成富翁的？
B: I don't know. It couldn't have been easy though.
不知道，肯定很不容易。