Please note:
If your architecture is i686 or x86 (32-bit) (what Debian & Ubuntu both refer to as i386) then Lubuntu 18.04 LTS was the end-of-road for Lubuntu.
Later Releases (18.10 & 19.04)
Yes we released Lubuntu 18.10 with the modern LXQt desktop. Lubuntu even produced alpha ISOs into the disco (19.04) cycle, which if installed, package updates were provided until 19.04 reached EOL (though Lubuntu never officially supported disco/19.04 in i386), however both 18.10 & 19.04 reached EOL long ago meaning Lubuntu 18.04 LTS was the last i386 system supported.
Can I continue using it ?
Yes you could, I’d suggest fully exploring your support status using ubuntu-support-status. Packages found in the ‘main’ repository will still get security updates, where you’ll note firefox still get security updates 
even if your desktop & many apps are now unsupported.
The risk is your decision, however if you have questions (understanding ubuntu-support-status or other), you can ask and I’ll give my thoughts/opinion in most cases.
What are my alternatives ?
There are a few; myself I also test (and love) Debian so it’s all I’ll suggest. I tested Debian 10/Buster on my i386 hardware, and performance was on most boxes very similar (on my lowest powered box Lubuntu 18.04 well outperformed Xubuntu or Debian 10/Buster but on most hardware the performance difference was very small).
Debian 10/Buster has more of it’s life left than Lubuntu 18.04 LTS so it would be my main alternative if you’re forced to use a i386 box.
(I still use i386 boxes; but almost all my online tasks are performed on much more modern amd64 hardware)