Chances of pregnancy

So I take my pill continuously for 3 months then break. I've just had my break and withdrawal bleed, slightly lighter than usual but had it. I've just changed birth control but had sex about an hour before taking my new pill. What are the chances of getting pregnant. Could you ovulate that soon and also would I be protected by the new pill or does it have to get into your system first. I've changed from microgynon to desogestrel.

Thank you

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