ups：好調なこと、好調な時。一回ではなく何回も繰り返すので複数形です。
downs：不調なこと、不調な時。これも同じく"s" をつけます。
up, down は本来、形容詞や副詞として使いますが、ここでは"s" をつけることで名詞になります（意味は上記参照）。
「Every job has its good and bad points.」（どんな仕事にも長所と短所がある）というフレーズもあります。
When someone asks you "How is work?", saying that you have "ups and downs at work", means that sometimes you have a good day and sometimes you don't. Sometimes you feel great, you love your job, etc., and sometimes you have bad days, when you don't enjoy yourself at work, maybe it is hard, boring, you lack enthusiasm, etc.
Saying that your "feelings towards work vary", is another way of saying that you have good days and bad days. It implies that your attitude and feelings towards work change on a regular basis, that you do not consistently feel neither overall "good" nor "bad", but that it depends on the day.
The verb "to vary" means that something is subject to change. This can be used to say that things are sometimes good at work and sometimes they are not, because it implies that how you feel at work changes on a day to day basis.
"How is work?"（仕事はどう）と聞かれ、"I have my ups and downs at work" と答えると、
「良い日もあればそうでない日もある」
「すごく楽しくてやりがいを感じるときもあるし、良くない日、楽しくないとき、辛いとき、退屈なときもある」
という意味になります。
"My feelings towards work vary" も「良い日もあれば悪い日もある」と伝える言い方です。これは、
「仕事に対する気持ち・考えはいつも変化している」
「常に『良い』とか常に『悪い』ではなく、日によって変わる」
というニュアンスです。
動詞の "to vary" は「変化する」という意味です。「仕事では良いときもあれば悪いときもある」と伝えるときに使うことができます。これは、仕事に対する気持ちが日々変化しているというニュアンスになります。
"Not so good" means more or less bad. When telling someone who asks you how is work and you reply with this, be sure to have reasons on why its good or bad as they're sure to ask why.
"Not so good" は「あまり良くない」という意味です。
「仕事はどうか」と聞かれて、このように答えるなら、その理由も準備しておいてください。相手は必ず聞いてくるので。
It depends on the day. Some days are good and some days are bad.
We use the phrase " it depends on" very frequently to talk about a variable situation, like the weather. This will help you listener to understand that it isn't all good or bad. I hope that this helps! :)
These three phrases can be used to express that every day at work and be different and it depends more on what our work day has in store for us.
"Ups and downs" can be a good expressional way to describe that there are some, "good days and bad days."
Along with saying, "so-so," describes that things can be quite average, not good but also not bad either.
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