、！
Lately I hadn't been able to sing because a lot has been going on, so today I sang my heart out!
Literal
Recently various existed [because-から] could-not-sing [because-から], today [topic-は] sang-the-hell-out-of-it!
A relief/release sentence. いろいろあって ('various things happened,' 'a lot going on') is a vague catch-all that signals 'for complicated reasons I'd rather not specify.' 歌いまくる is a compound verb using the auxiliary ~まくる, which means 'to do X to an extreme, all out, without restraint' — a register-marked intensifier. 食べまくる (eat everything), 買いまくる (buy everything), 歌いまくる (sing your heart out). The connotation is 'unrestrained, maximal effort.' Distinct from ~続ける ('continue') — まくる is about intensity and excess, not just duration.