Try some foreplay before you go for sex,
might be some feminie seduction will help...:)
Although Sex power starts decreasing in mens from the age of 35 but at this age not that much that it could stop him from doing sex. There is nothing like menopause in mens. Getting weak erection of penis could be because of many reasons. One of the main reasons at this age group could be anexity and depression which slowly ends up in decreasing testrosone levels in blood and other harmonal balances causing this. The other reasons could be High or Low Blood Pressure also which you never know you have and is very serious too. So better visit A Cardiologist to get Heart chekup first followed by an Endochronologist who might get your harmones levels like Serum Testostrone, T3, T4, TSH, FSH, LH and Prolactin checked and a Psychiatrist who might check you up for Anexity and or Depression related problems. Once exact reasons has been identified, do the teatment and he will be alright. Do visit all of them to reduce any chance of misdiagnosis or incomplete diagonosis and tell all the Doctors very clearly that this is the problem and you want to get checked up to for every possible cause. Generally it takes few months to get ok so be patience also while getting treated. Also do not feel shy when when going to a Doctor because he is 42 and you are 30. Afterall he is your husband and father of your childs.