What kind of contraception is better to use?

Patient's question:

Hello! Since my son is only 5 months old now, he cannot take oral contraceptives. I don't know which contraceptive method would be better. I heard there is something called a "long-acting contraceptive injection." I'm wondering if it can be used during breastfeeding?
First follow-up question: First of all, thank you, Dr. li1106. I heard that there could be allergic reactions after inserting an IUD, so I didn't dare to do it. Could anyone tell me about long-acting contraceptive injections?
Second follow-up question: Hello, Fangyu, I didn't expect long-acting contraceptive injections to be so troublesome. I just wanted to ask you one more thing—do they have any impact on the child?

Doctor's answer:

Hello, the long-acting contraceptive injection, also known as Contraceptive Injection No. 1, provides one month of contraception with a single injection.
Usage: In the first month, inject 2 vials. This can be done on the 5th day of menstruation by simultaneously injecting 2 vials, or by injecting 1 vial on the 5th day and another on the 10th day. For the second month and beyond, inject 1 vial within the 10–12 days of menstruation. The long-acting injection should be administered as a deep intramuscular injection. In rare cases, some individuals may experience an allergic reaction. After injection, wait for 15 minutes before leaving.
During the course of treatment, if menstruation is prolonged, additional short-acting contraceptive tablets (No. 1 or No. 2) can be taken, with 1–2 tablets daily for 4 days. If menstruation is shortened, start taking No. 1 or No. 2 tablets 10 days after injection, with 1–2 tablets daily for 4–6 days. For women with amenorrhea, the next injection should be administered 28 days after the last injection. If amenorrhea persists for 2 consecutive months, the injection should be discontinued. If the long-acting contraceptive injection has been used for an extended period, continue taking short-acting oral contraceptives for 3 consecutive cycles after discontinuation to prevent menstrual irregularities.