advice

Ok feel weird talking about bowl movements but I'm 20w almost 21 weeks 
I haven't gone in 4 weeks 
doctor gave me some stuff to help it ain't working any advice 
I can't sleep and I no longer feel hungry haven't felt hungry for a few days forcing myself to eat 
My normal diet is mostly fruit/veg as I crave them 
I drink a lot of water and gave up coffee around week 9 of pregnancy 
I also have a urine track infection first one Iv ever had and have been put on anti biotics 
Last time I had antibiotics I got rely constipated and I fear I won't go for even longer