I applied for a patent without authorization. During this period, others used my technology to produce products and imitate me. Is it infringement?

No, according to Article 11 of the Patent Law:

After the patent right for invention and utility model is granted, except as otherwise provided in this Law, no unit or individual may exploit the patent without the permission of the patentee, that is, it may not manufacture, use, promise to sell, sell or import the patented product for production and business purposes, nor may it use the patented method and use, promise to sell, sell or import the product directly obtained according to the patented method. After the design patent is granted, no unit or individual may exploit its patent without the permission of the patentee, that is, it may not manufacture, promise to sell, sell or import its patented product for production and business purposes.

That is, the patent right takes effect from the date of authorization, and it does not belong to infringement before that. However, if it is an invention patent, and it has been made public before the authorization, there is temporary protection between the disclosure date and the authorization date, during which the other party can be required to pay reasonable infringement fees.