how soon is to soon

I Have raise my credit score from a 514, 522and 520 to 610,620 and 620 in 3months. I have paid all my bills, but have three paid after charge offs on my credit report. however been able to open a new credit card...I know that i need three open lines of credit to get a good score, but is it to soon to apply for another card...(I open my card in april)
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i would try it for suremy wife always tells me to get my ostrich head out of the hole