Progesterone, what should I do?

Hi! For more than two years I've experienced spotting and sometimes light bleeding for 1-2 weeks before my period. Orally taken progesterone pills didn't help, so I was directed to a fertility clinic after TTC for more than a year without any success (not even a hint of pregnancy). After the first IUI and taking 200 mg progesterone vaginally once per day, I'm now 16dpo and pregnant. No sign of spotting. I was told that I can now quit the progesterone but I'm terrified of the thought as I've read that the placenta doesn't start to produce its own progesterone until 8-12 weeks. If I've had insufficient levels without the medication, can I really trust that now the level is enough to sustain the pregnancy even without support?