PT- Advice

[Solid]

Hello everyone,

I'm not sure this is the right forum for this question, but it was the one forum that I knew of with a PT thread in it already. I apologise sincerely if it's in the wrong place.
Since August I have been doing a high level of bodyweight-only training consisting largely of push-ups, sit-ups, pull-ups and running. As an apparent result of this training, I have lost a lot of the muscle mass I had before I began, in exchange for muscle strength. This body type was ideal for what I was doing at the time. However, now I want to play Rugby, which requires a lot more muscle mass. As such, I have started weight training again, three times a week. However, I am maintaining my 300 press ups 200 sit ups 'core strength' five-times-a-week regime. I was wondering if these 'core strength' exercises would prevent or slow the growth of my muscle mass?
If so, is there a level of 'core strength' training which I can maintain that will not jeapordize my muscle-mass training?

Thank you and again I apologise if this is in the wrong place,

Solid