Do you have problems inserting a finger or two into your vagina? What about toys? Any difficulty with penetration?
If it isn't that he's "hard enough" (and a workable erection feels like anything from a slightly squishy on the outside with a firm core silicone toy to a rod of something resembling steel with skin over it. Every man is different and every man can have varying erections.) there is a condition called "Vaginismus." It is when muscles around the opening of the vagina spasm and prevent penetration or make this very painful. Only a doctor or midwife can diagnose Vaginismus.
Is this a new problem or has it always happened? I'm not sure what you mean by "he can't get in." Does his penis kind of moosh when it comes in contact with your vulva (which is usually what happens when the erection is lacking or not strong enough)or is he trying and has an erection, and nothing can enter the vagina?
Oral sex for and by both of you will help with arousal so that penetration will be easier. I've been having sex for decades, and have no problem with my vaginal muscles, but I need to be "warmed up" and get the natural lubrication going (often to orgasm) by receiving oral sex. Also, My Man is older (in his early 50s) and he almost always needs (but always gets) some oral sex from me before and even during PIV sex. Sometimes you just want to change things up, and we go back and forth.
Both your natural lubrication and a good, safe bottled lube (my new favorite is Sliquid Ride H2O) applied to both your vagina and his penis before penetration is started, after a good oral session may do the trick.
If not, then doctor visits for both of you is probably a good idea.
