Kate Middleton is trying to keep calm and carry on amid her cancer battle. “Part of her day-to-day routine is trying to get her strength back,” a source dished about the mom-of-three, who shares Prince George, 10, Princess Charlotte, 8, and Prince Louis, 5, with husband Prince William. “She’s going through her treatments, which include chemotherapy, so she’s not supposed to push herself too much,” the insider added. “Kate’s anxious to get back to juggling royal duties and the children, but that will take some time.” During this tough time period, Kate, 42, is fortunate to lean on her loved one…