Even though I'm female I barely have any physical sensation "down there" (I'm a T4 para) at the same time I do get sensation from stimulation when having sex with my husband, but very little to none from masterbation. Orgasm is a funny thing, in that, not everyone acheives it all the time and sometimes not at all. It doesn't mean there is anything wrong or that you can't or won't be able to ejaculate or climax. So, don't doubt if you can or can't climax since you won't know if you can without experimentation and finding out what works for you.
Have you payed attention to what has "caused" the ejaculation such as how your holding it, the pressure you've used and wether fast, slow or a combination of movements and pressures has provided the results you're looking for when you ejaculate. Also, the more you think about it and try to achieve it can make it harder for you to get the results you want. Do you have someone that can help you experiment in finding out what does and doesn't work? You already know the important part that you can ejaculate. Now it's just a matter of finding out what works for you. Also, if you're comfortable with having someone else/a partner help you find those things that really get you the results you're looking for that just may be the ticket.
The main thing is to take your time and try not to think to hard about it. Some Women have the same problem with masterbation, they try to hard and think to much about it, so in turn they don't climax, orgasm or ejaculate (and yes, women do ejaculate) So, It could just a matter of the more you think about it the less likely you are to orgasm or climax for that matter. One more thing, if you're willing to have a partner help you try to see if maybe the nipple stimulation while masterbating helps. Just make sure the partner you choose is patient and willing to help out. Another thing that might help is try going to a xxx store and they should have some toys for men that vibrate that you can use while masterbating that may help as well.
Hopefullly there are other people on here that can help you better than I can, good luck and I hope things work out for you