The word "just" is better than "only" in your sentence. Also, remove the word "that" in "that I can understand" and add a comma after "past": "Oh god, I think my English has improved a lot. I could not understand most of the lyrics of English songs and had to look at the lyrics in the past, but now I can understand most of them just by listening to them."

"Oh god" is not usually used to start a sentence like this. If you want to use an expression to start the sentence you coud say "Thankfully" I think .... or I'm pleased to say that I think. ....

Thanks, I will keep that in mind!!!

I think my English has improved a lot. In the past I could not understand most of the lyrics unless I was looking at them. Now I can understand most of them just by listening to them. I don't think you need the "Oh, god" at the beginning of the sentence. Some people would be offended if you use the word "God" in this manner. Your second sentence is rather long, so I made it into two sentences. "I could not understand most of the lyrics ...and had to look at the lyrics." You don't need to say "lyrics" twice in the same sentence, so I substituted "them" for "lyrics." I agree that #1 is better than #2.

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