要视具体语境而定，如果表示有很多担忧，此时worry为不可数名词，就用a lot of worry
如果表示有很多糟心事、烦心事，此时worry为可数名词，就用a lot of worries
附上牛津词典的解释和例句：
noun
1.[U]?担心；忧虑；发愁
the state of worrying about sth
同义词：?anxiety
The threat of losing their jobs is a constant source of worry to them.
丢掉工作的威胁时常使他们忧心忡忡。
to be frantic with worry?
愁得要命
2.[C]?~ (about/over sth) | ~ (for/to sb)
令人担忧的事；让人发愁的事
something that worries you
family/financial worries
家庭中的 / 财务上的烦恼
worries about the future
对未来的担忧
Mugging is a real worry for many old people.
行凶抢劫确实令许多老人心神不安。
My only worry is that…
唯一令我担忧的是…