Horse gained lots of weight in a month?

well it soundes like my mare coz she was getting turn out and coz ive got to tall for her now she goes on the lungs every other day but she turn out to be in foal and six weeks later she had a little colt she if the wieght dosent go i would call a vet out to check her over coz you dont want to be fooled like me coz i dident evn have a stallion it was my so called gelding that wasent cut propley.lol.( i dont mind having a little foal tho) keep an eye out for things like teats getting big and getting grumpy and looking a bit pear shaped and getting restless. x