Hi there. Strengthening your lower abdominals (transversus abdominis) may help. Plus pelvic floor muscle exs. You may find a maternity belt helpful as it gives a little compression around the pelvis. As happyrunning said, the pelvis loosens, due to the pregnancy hormones and you can get too much movement or differences in movement.
There is a generic term - pregnancy related pelvic girdle pain - for problems around the pelvis during pregnancy. The Association for Chartered Physiotherapists in Women's Health (put ACPWH or the full thing into google) has a section on leaflets. You can download the one on pregnancy related pelvic girdle pain. (Used to be called symphysis pubis dysfunction).Don't think it has much specific on running, but loads of advice for daily life and advice re sources of help and support. Your problem may come under this umbrella term, but you ideally need assessment by a relevant health professional.
I don't have much experience of osteopathy, and happyrunning has already given details re that. However, physiotherapy can help a lot too. Get your GP to refer you for assessment, the earlier the better really. Core stability exs can really help, plus they will hopefully give loads of advice. Sometimes recruiting lower tummy muscles andglutes when you are running can make things feel more comfy but you really need someone to do a full individual assessment so that advice is specific and right for you.
Hope you get on okay.