Cerberus's answer makes sense, but it's important to remember that this letter wasn't originally written in Latin, but Greek. The Greek text, from the SBH edition, reads:
Ἐχάρην δὲ ἐν κυρίῳ μεγάλως…
The Vulgate, in this case, is an extremely literal translation of the Greek. The first Greek word, ἐχάρην, is aorist, so the Latin likewise uses an aorist (which looks identical to the perfect but is slightly different).
Scanning through LSJ's attestations for χαίρω, I haven't found any instances of an aorist with a present meaning; as you would expect, the meaning is generally past. And so indeed, the New International Version renders this with a past meaning in English:
I rejoiced greatly in the Lord…
And likewise the King James version:
But I rejoiced in the Lord greatly…
Wait, but the Greek verb isn't deponent, so why does the Greek use a passive form? Χαίρω is more often found in the active, so we might expect an active ἐχαίρησα instead. However, according to LSJ, the active, middle, and passive of this verb are not infrequently used with the same meaning:
Pass. (in same sense), aor. 2 ἐχάρην [α^] 7.54, etc.
In other words, the second aorist passive ἐχάρην is used with the same sense as the active, and shows up in Iliad 7.54 among other places. In cases like this, where an active, middle, and passive form were all available, there was probably some subtle difference in meaning or connotation that led Paul to choose one over the other. But whatever that difference was, LSJ doesn't mention it.
For the "now", that's a translation of the second word of the Greek, the particle δὲ. It's an extremely versatile particle with a lot of possible meanings, so while autem may be the closest Latin equivalent, it's not an exact translation.
