When would my dog start "showing" if she is pregnant?

My dog is a pitbull/boxer mix. She is 11 months old and she went into heat about 3 1/2 weeks ago. She stays in the backyard during the day and we have an underground fence so even though she cant get out, other dogs are still able to get in.

Everyone I’ve talked to so far says she should only be in heat for about 2 weeks. Her lady parts have been swollen since she started and it hasnt gotten any better. Now her nipples are swelling too and she has started breathing really heavy all the time. She is always trying to get into her food bag like she is starving or something. That is not normal for her, she is usually very well behaved.

I’m not sure if these are early signs of pregnancy or if it would have even been long enough for her to have symptoms of being pregnant yet. I’m taking her to the vet next Monday but I’m still curious so I have an idea what to expect when we get there.

Any advice helps so thanks in advance! Cheers!