Inserting an internal condom (female) should get easier the more you do it. Try practicing putting it in when you are not about to have sex so that you get used to it.
Still not working? If it does not get any easier to insert and you are concerned about STIs, go with external condoms (male) instead.
If STI protection is not a concern for you right now, you might want to move toward contraception that does not require you to insert anything. The IUD and The implant are both inserted in a clinic.
Try a different method: implant; IUD.