Hi Min

Your lower back pain is caused by a change in your centre of gravity. And this is caused by your growing tummy making you lean a little backwards when you stand/walk. Try to think about your posture. A good massage can help relieve the pain.
Your achy hips are caused by your hormones starting to loosen all your joints and ligaments. These hormones will also be contributing to the back pain.
Leg cramps are very common and usually a result of a lack of potassium / sodium / and or magnesium.
Constipation is again caused usually by your hormones slowing down the passage o food in your intestines. When food passes slowly through your gut your body takes more water from it making your stools hard and dry. To help prevent this you need lots of fibre in your diet. You also need to drink lots of fluid to make the fibre work.
Ok to get things moving try prune juice of pear juice. If this does not help then go to the chemist and get some colyxl and senna take 2 in the morning and 2 at night They can take up to 48 hours to work.