Why is my cat changing? 10 points?

i have a mix female cat and she is the sweetest thing. when u clap ur hands she hides, and she plays fetch, and eats everything. but i great thing about her was that she always uses the litter box. i i clean it everyday or once every 3 days, she goes. she is 2 and a half years old and on januray 14th was her first kitty magic, and after dat she is so different. we resued a male cat on october and we got rid of him in janurary. she was so scared of him, untill the 14th when she went in heat, so then we gave him to a local shelter. but after that she is different, like she used to go into heat once every 3 or 4 months, now its every 2 weeks. and now when u clap ur hands, she donsent hide anymore. and the other day she did not go in the litter box. i dont thing its uti because there is no blood, and she does not cry when cleaning herself down there. and its not worms cuz there is no "rice" in her poop her her but area. we did change the litter, so we r ganna change it back soon, to see if she goes back in the box. but y would she go in heat every 2 weeks, that was never normal for her. and i cant take her to the vet, cuz of money poblems, and dont say things liek im a bad cat onwer cuz i cant take her to the vet, cuz i no plenty of ppl dat take good care of there pets and they never went to the vet. also she was fine untill about 8 weeks after the kitty magic and then she started going into heat every 2 weeks. so can it be from a miscarrage, cuz she did start eating a lil moe, but not much, and then after about 8 weeks, she is going into heat constanly, but its not her normal heat cyle, like before she used to go into heat every 3 months, and it was nonstop meowing, now its just a few moews and some of the weird walking, and then she stops for a while and then starts back up. plz help.......10 points