Hi Instant. It's probably too late, but you should have held off tossing the mom Citrus. As long as it had oranges, it was alive.

Most likely, the original tree was grafted. The seedling you sowed isn't. Right?

Grafted Citrus have certain advantages seed-grown doesn't. For one, grafted trees flower and fruit sooner than seed grown. Grafted trees start fruiting 2-3 yrs of age. Seedlings can take up to 14 yrs. It depends.

If possible, you should place your Orange outdoors in summer.
How much light is it getting indoors? Citrus should be set directly in front of a south or west window.

Citrus fertilizer is best, but if you can't find it, a high nitrogen fertilizer will do.

Proper watering is very important. Never keep soil soaking wet. Let dry between waterings, especially during winter months.

Some humidity and fresh, circulating air is important.
Dry, stuffy rooms cause problems.

When young, citrus should not be potted in huge containers. Allow roots to grow. When they fill pot, repot in a container 1-2 sizes larger.

Now that winter is nearing, place your citrus in the sunniest window in your home. Preferably a cool room. Never exceed 75F degrees.
Indoor/gas heat, not outside temps.
Also, do not put a plant directly in front of a heating vent.

Do you have a photo? How large are the thorns? Toni